digitonin and 3-((3-cholamidopropyl)dimethylammonium)-1-propanesulfonate

To conduct biochemical studies in vitro, membrane proteins (MPs) must be solubilized with detergents. While detergents are great tools, they can also inhibit the biological activity and/or perturb oligomerization of individual MPs. Nanodisc scaffold peptide (NSP

Topics: Amino Acid Sequence; Animals; CHO Cells; Cholic Acids; Cricetulus; Detergents; Digitonin; Humans; Peptides; Protein Domains; Protein Multimerization; Sterol O-Acyltransferase; Surface-Active Agents

Membranes prepared from rat brain were treated with increasing concentrations of cationic, neutral, anionic and zwitterionic surfactants. Potent inactivation of [(3)H]MK-801 binding to NMDA receptors (NRs) was provided by the cation cetyl pyridinium (IC50 25 μM) and the neutral digitonin (IC50 37 μM). A 2 h incubation of rat brain membranes at 24°C with 100 μM of the neutral Triton X-100 resulted in about 50% reversible inhibition (without inactivation). Reversible inhibition was also effected by the anion deoxycholate (IC50 700 μM), and by the zwitterions N-lauryl sulfobetaine (12-SB(±), 400 μM) and CHAPS (1.5 mM), with inactivation at higher concentrations. Keeping the NR cation channel in the closed state significantly protected against inactivation by cations and by 12-SB(±), but not by the other detergents. Inactivation depended differentially on the amount of the membranes, on the duration of the treatment, and on the temperature. Varying the amount of membranes by a factor 8 yielded for cetyl trimethylammonium (16-NMe3(+)) IC50s of inactivation from 10 to 80 μM, while for deoxycholate the IC50 of inactivation was 1.2 mM for all tissue quantities. Some compounds inactivated within a few min (16-NMe3(+), digitonin, CHAPS), while inactivation by others took at least half an hour (Triton X-100, deoxycholate, 12-SB(±)). These last 3 ones also exhibited the steepest temperature dependence. Knowledge about the influence of various parameters is helpful in selecting appropriate conditions allowing the treatment of brain membranes with amphiphiles without risking irreversible inactivation.

Topics: Animals; Cell Membrane; Cerebral Cortex; Cetrimonium; Cetrimonium Compounds; Cholic Acids; Deoxycholic Acid; Detergents; Digitonin; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Hippocampus; Male; Octoxynol; Quaternary Ammonium Compounds; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

Mitochondrial outer membrane Bax oligomers are critical for cytochrome c release, but the role of resident mitochondrial proteins in this process remains unclear. Membrane-associated Bax has primarily been studied using 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) as the solubilizing agent, as it does not induce conformational artifacts, although recent evidence indicates it may have other artifactual effects. The objective of this study was to investigate digitonin as an alternative detergent to assess Bax oligomeric state, and possible interaction with voltage-dependent anion channel (VDAC)1 in cerebellar granule neurons. VDAC1 co-immunoprecipitated with Bax in digitonin extracts from healthy and apoptotic neurons. Two-dimensional blue native-SDS-PAGE revealed five Bax and VDAC1 oligomers having similar masses from 120 to 500 kDa. The levels of two VDAC1 oligomers in Bax 1D1 immunodepleted extracts negatively correlated with levels of co-precipitated VDAC1, indicating the co-precipitated VDAC1 was derived from these oligomers. Immunodepletion with the 6A7 antibody modestly reduced the levels of Bax oligomers from apoptotic but not healthy neurons. A sixth 170 kDa oligomer containing exclusively 6A7 Bax and no VDAC1 was identified after apoptosis induction. CHAPS failed to solubilize VDAC1, and additionally yielded no distinct oligomers. We conclude that digitonin is a potentially useful detergent preserving Bax-VDAC1 interactions that may be disrupted with CHAPS.

Topics: Animals; Animals, Newborn; bcl-2-Associated X Protein; Cerebellar Cortex; Cholic Acids; Cytoplasmic Granules; Digitonin; Neurons; Primary Cell Culture; Rats; Rats, Wistar; Solubility; Voltage-Dependent Anion Channel 1

Cell-free expression has become a highly promising tool for the efficient production of membrane proteins. In this study, we used a dialysis-based Escherichia coli cell-free system for the production of a membrane protein actively integrated into liposomes. The membrane protein was the light-driven proton pump bacteriorhodopsin, consisting of seven transmembrane alpha-helices. The cell-free expression system in the dialysis mode was supplemented with a combination of a detergent and a natural lipid, phosphatidylcholine from egg yolk, in only the reaction mixture. By examining a variety of detergents, we found that the combination of a steroid detergent (digitonin, cholate, or CHAPS) and egg phosphatidylcholine yielded a large amount (0.3-0.7 mg/mL reaction mixture) of the fully functional bacteriorhodopsin. We also analyzed the process of functional expression in our system. The synthesized polypeptide was well protected from aggregation by the detergent-lipid mixed micelles and/or lipid disks, and was integrated into liposomes upon detergent removal by dialysis. This approach might be useful for the high yield production of functional membrane proteins.

Topics: Bacteriorhodopsins; Cholates; Cholic Acids; Digitonin; Escherichia coli; Liposomes; Phosphatidylcholines; Protein Biosynthesis

Solubilization is the most critical step in the purification of opioid receptors as these proteins are highly sensitive to detergents and get inactivated even with very mild detergents. Membranes enriched with micro-opioid receptors from bovine corpus striatum were solubilized by various methods to obtain the active soluble receptor suitable for affinity purification. Solubilization by digitonin resulted in marginal yields. CHAPS in presence of NaCl could extract active receptor into the solution. The detergent and NaCl were removed by either polyethylene glycol precipitation or by desalting on Sephadex G50. The polyethylene glycol precipitation resulted in the formation of liposomes into which the receptor protein was incorporated. Liposome formation was not observed in desalting method and the recovery of the receptor was partial.

Topics: Animals; Brain; Cattle; Cholic Acids; Chromatography, Affinity; Detergents; Digitonin; Liposomes; Membranes; Polyethylene Glycols; Receptors, Opioid, mu; Salts; Sodium Chloride; Solubility; Temperature

In pollen tubes of Nicotiana alata, a membrane-bound, Ca(2+)-independent callose synthase (CalS) is responsible for the biosynthesis of the (1,3)-beta-glucan backbone of callose, the main cell wall component. Digitonin increases CalS activity 3- to 4-fold over a wide range of concentrations, increasing the maximum initial velocity without altering the Michaelis constant for UDP-glucose. The CalS activity that requires digitonin for assay (the latent CalS activity) is not inhibited by the membrane-impermeant, active site-directed reagent UDP-pyridoxal when the reaction is conducted in the absence of digitonin. This is consistent with digitonin increasing CalS activity by the permeabilization of membrane vesicles. A second group of detergents, including 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate (CHAPS), Zwittergent 3-16, and 1-alpha-lysolecithin, activate pollen tube CalS 10- to 15-fold, but only over a narrow range of concentrations just below their respective critical micellar concentrations. This activation could not be attributed to any particular chemical feature of these detergents. CHAPS increases maximum initial velocity and decreases the Michaelis constant for UDP-glucose and activates CalS even in the presence of permeabilizing concentrations of digitonin. Inhibition studies with UDP-pyridoxal indicate that activation by CHAPS occurs by recruitment of previously inactive CalS molecules to the pool of active enzyme. The activation of pollen tube CalS by these detergents therefore resembles activation of the enzyme by trypsin.

Topics: Cholic Acids; Detergents; Digitonin; Enzyme Activation; Glucosyltransferases; Membrane Proteins; Nicotiana; Plants, Toxic; Pollen; Pyridoxal Phosphate; Schizosaccharomyces pombe Proteins; Trypsin; Uridine Diphosphate

The compartmentation of nucleoside diphosphate kinase (NDPK) was studied in mitochondria isolated from heart and liver of rat, rabbit, and pigeon. Compartmentation was assessed by determining latencies of enzyme activities, fractionating mitochondria with digitonin, and treating mitochondria with trypsin in the presence and absence of digitonin. NDPK activity in pigeon liver mitochondria was five- and seven-fold higher than in rat and rabbit liver mitochondria. The ratios of NDPK activities in liver vs. heart mitochondria were about 15 for rat, 2 for rabbit, and more than 40 for pigeon. Nearly all NDPK in pigeon liver mitochondria is in the matrix space, but outside the matrix in rat and rabbit liver mitochondria. Most NDPK in pigeon heart mitochondria was located outside the matrix while a significant fraction may be in the matrix of rat and rabbit heart mitochondria. These results are discussed relative to the assumed role that mitochondrial NDPK transfers the phosphoryl group of GTP produced in the Krebs cycle to the adenine nucleotide pool.

Topics: Animals; Cell Fractionation; Cholic Acids; Columbidae; Digitonin; Female; Male; Mitochondria, Heart; Mitochondria, Liver; Nucleoside-Diphosphate Kinase; Rabbits; Rats; Rats, Sprague-Dawley; Trypsin

The solubilization of rhodopsin and phospholipids from disks prepared from bovine retinal rods was studied using five different detergents. The relative amounts of rhodopsin and lipid extracted during membrane solubilization differed dramatically with the nature of the surfactant; the two nonpolar detergents, Emulphogene (polyoxyethylene-10 tridecylether) and octylglucoside, removed more protein than lipid; two bile salt-related detergents, 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (Chaps) and taurocholate, released relatively more lipid than protein; and digitonin, which shares characteristics with both groups of detergents, extracted more lipid per mole of rhodopsin than the former two but less than the latter two. Solubilization was temperature-dependent with all five detergents, though particularly so with octylglucoside: concentrations adequate for the total micellation of disks at 23 degrees C were ineffectual at 4 degrees C. In total solubilizates of disks, the amount of lipid recovered in rhodopsin-lipid-detergent micelles showed a closer correlation with the critical micellar concentration (CMC) than with the chemical nature of the detergent (octylglucoside > taurocholate > Chaps > digitonin > Emulphogene). The higher the CMC, the larger the amount of lipid associated to the solubilized rhodopsin and the larger the amount of lipid reassociated to rhodopsin upon surfactant dilution. For all five detergents, the lipid progressively extracted from disks during solubilization was relatively richer in phosphatidylcholine (PC) than the lipid in the original membranes. The lipid which tended to be associated with rhodopsin in protein-lipid-detergent mixed micelles was also consistently richer in PC than that present in lipid-detergent micelles. Bleaching of solubilized rhodopsin decreased the amount of lipid in protein-lipid-detergent micelles. Rhodopsin photolytic transitions were faster in nonionic than in bile salt-related detergents.

Topics: Animals; Cattle; Cholic Acids; Detergents; Digitonin; Glucosides; Light; Membranes; Micelles; Models, Chemical; Phospholipids; Polyethylene Glycols; Rhodopsin; Rod Cell Outer Segment; Solubility; Spectrophotometry; Taurocholic Acid; Temperature

We previously demonstrated that nonesterified as well as esterified eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) inhibit U46619-induced platelet aggregation and [3H]U46619 specific binding to washed human platelets. It was also demonstrated that esterification of these fatty acids resulted in a decrease in the affinity of [3H]U46619 for the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor. In order to investigate the specificity of this inhibition, the effects of 20:5n-3 and 22:6n-3 on the function and binding of the platelet alpha 2-adrenergic receptor were studied. It was found that neither 20:5n-3 nor 22:6n-3 (nonesterified or esterified) altered epinephrine-induced aggregation or [3H]yohimbine specific binding. Moreover, Scatchard analysis revealed that esterification with either 20:5n-3 or 22:6n-3 did not alter the dissociation constant for [3H]yohimbine binding. Modulation of the TXA2/PGH2 receptor by 20:5n-3 and 22:6n-3 was next evaluated using CHAPS- and digitonin-solubilized platelet membranes. [3H]SQ29,548 dissociation constants of 26.5 nM and 20.8 nM were measured for CHAPS and digitonin-solubilized membranes, respectively. Competitive binding experiments in these solubilized preparations revealed that 20:5n-3 or 22:6n-3 blocked [3H] SQ29,548 binding with IC50 values in the range of 6-15 microM, while concentrations of these fatty acids of up to 100 microM showed no effect on [3H]yohimbine binding. On the other hand, the IC50 values for inhibition of [3H] SQ29,548 binding by linoleic acid (18:2n-6) and gamma-linolenic acid (18:3n-6) were in the range of 150 microM. Furthermore, 18:2n-6 and 18:3n-6 showed similar inhibitory effects on [3H]yohimbine binding. Finally, competition binding studies performed in a partially purified TXA2/PGH2 receptor preparation also demonstrated inhibition of [3H]SQ29,548 binding by 20:5n-3 and 22:6n-3. Collectively, these findings support the notion that 20:5n-3 and 22:6n-3 can selectively and directly modulate TXA2/PGH2 receptor function, and that this mechanism of action may contribute to the antiplatelet activity associated with diets rich in these fatty acids.

Topics: Blood Platelets; Bridged Bicyclo Compounds, Heterocyclic; Cell Membrane; Cholic Acids; Detergents; Digitonin; Docosahexaenoic Acids; Eicosapentaenoic Acid; Fatty Acids, Unsaturated; Humans; Hydrazines; Platelet Aggregation; Platelet Aggregation Inhibitors; Prostaglandin Endoperoxides, Synthetic; Prostaglandins H; Receptors, Prostaglandin; Receptors, Thromboxane; Receptors, Thromboxane A2, Prostaglandin H2; Thromboxane A2

Binding of platelet-activating factor (PAF) to a specific high-affinity membrane receptor has been demonstrated in numerous cell types, but very little is known about the molecular nature of this receptor. The receptor from rabbit platelets was solubilized using CHAPS, digitonin, octyl glucoside, Nonidet P-40 or sodium cholate, either with pre-bound [3H]PAF or in the absence of ligand. We have been able to demonstrate for the first time that the receptor solubilized with CHAPS, in the absence of ligand, could retain its binding activity. It migrated as a high molecular mass complex (greater than 350 kDa) on a Bio-Gel A-0.5 m gel filtration column. Binding to solubilized receptor rapidly reached an equilibrium at room temperature, but was much slower at 0 degrees C. Scatchard plots were used to calculate the number (approx. 100 per cell) and the affinity (Kd 2.5 +/- 1.4 nM) of the solubilized receptors. These values were comparable with those obtained from whole-cell binding experiments. Competition by PAF antagonists also verified that the assay was measuring PAF receptor binding activity. The presence of a protein in the receptor complex was demonstrated by heat and trypsin inactivation of binding activity. Trypsin had no effect on binding of PAF to whole cells, but was able to decrease binding activity in solubilized receptor preparations. Attempts to demonstrate the involvement of a glycoprotein by use of various lectin columns proved unsuccessful. The latter results are consistent with findings suggesting that the binding site of the PAF receptor may not be exposed at the cell surface.

Topics: Animals; Binding, Competitive; Blood Platelets; Cholic Acids; Chromatography, Gel; Digitonin; Platelet Activating Factor; Platelet Membrane Glycoproteins; Rabbits; Receptors, Cell Surface; Receptors, G-Protein-Coupled; Solubility; Trypsin

To investigate if G-protein-receptor interactions can be characterized using sucrose density gradients (SDG) we have determined the experimental conditions for muscarinic acetylcholine receptor (mAChR) solubilization and analysis on SDG. Solubilization of 65-80% of [3H]QNB bound mAChR was accomplished with 1% of detergent. Analysis of solubilized receptors on SDG containing 0.4 M KCl and 0.1% detergent demonstrated that the physical properties of the receptor-detergent complexes are influenced by the solubilizing detergent as well as detergents included in the SDG. Neither GTP gamma S nor NaF and AlCl3 altered the sedimentation properties of mAChR, suggesting that the solubilized mAChR is no longer associated with G-protein under these conditions. Receptors bound to [3H]oxotremorine and [3H]QNB had similar sedimentation properties, suggesting that, once solubilized, mAChRs do not remain associated with G-proteins. Covalent labeling with [3H]PrBCM followed by solubilization and analysis on SDS-gel electrophoresis demonstrated the presence of intact receptor molecule. These observations suggest that the changes in the sedimentation properties of detergent-receptor complexes are independent of G-protein interactions and are influenced by the nature of the detergent associated with the mAChR during analysis.

Topics: Animals; Cholic Acids; Digitonin; Filtration; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Male; Quinuclidinyl Benzilate; Receptors, Muscarinic; Solubility; Swine

Muscarinic receptors were solubilized by nonionic, zwitterionic and ionic detergents from porcine striatum. A mixture of digitonin and gitonin (3:2) was found to be most suitable in respect to receptor yield and stability. The solubilization of muscarinic receptors by this detergent appears to be dependent on the existence of free detergent micelles. Consequently, the receptor solubilization was studied at different protein-to-detergent ratios. Based on these experiments, a double extraction procedure was developed in which the receptor is solubilized subsequent to the solubilization of other membrane proteins. After elimination of the detergent excess, the binding of the receptor-detergent complex to six immobilized lectins was studied. In accordance with previous reports, we found a considerable portion of the digitonin/gitonin solubilized receptors (one step extraction procedure) specifically bound to wheat germ agglutinin via sialic acid residues. Muscarinic receptors solubilized by a double extraction procedure (either from porcine striatum or rat brain) did not bind to the lectin. This is not owing to selective extraction or partial denaturation, and indicates that considerable portions of the glycan residues are not covalently bound to the receptor polypeptide. A GTP-insensitive heterogenous agonist binding was found only at the non-wheat germ agglutinin binding receptors. The data analysis was performed by the affinity spectra method.

Topics: Animals; Brain Chemistry; Cholic Acids; Chromatography, Affinity; Detergents; Digitalis Glycosides; Digitonin; Micelles; N-Acetylneuraminic Acid; Protein Binding; Rats; Receptors, Mitogen; Receptors, Muscarinic; Sialic Acids; Solubility; Surface-Active Agents; Swine; Wheat Germ Agglutinins

The dihydropyridine receptor-calcium channel complex, prelabeled with (+)-[3H]PN200-110, was solubilized from rat heart membranes with a detergent mixture of digitonin and Triton X-100. The dissociation of (+)-[3H]PN200-110 was slow enough to permit the hydrodynamic characterization of the complex by means of sucrose gradient sedimentation and gel filtration. The hydrodynamic properties of the complex were determined in several detergents, including Tween 80, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid (CHAPS), and digitonin. S20,w values of 12.5, 15.4, and 21.0 S were obtained in sucrose gradients prepared in Tween 80, CHAPS, and digitonin, respectively. A Stokes radius of 86-87 A was obtained in each of the three detergents. Determination of the partial specific volume of the protein-detergent complex in each case revealed that the differences in S20,w values could be explained by the differences in the properties of the bound detergent species. Partial specific volumes of 0.796, 0.730, and 0.730 ml/g, corresponding to molecular weights of 595,000, 540,000, and 740,000 were obtained for the complex in Tween 80, CHAPS, and digitonin, respectively. This indicated that Tween 80 readily exchanged for the solubilizing mixture of digitonin and Triton X-100, whereas CHAPS did not. Detergent exchange with Tween 80 made it possible to determine the fractional contribution of the receptor protein to the molecular weight of the protein-detergent complex. The molecular weight of the dihydropyridine receptor-calcium channel complex was estimated to be 370,000. The protein-detergent complex was found to have a frictional coefficient of 1.39, consistent with a large transmembrane protein.

Topics: Animals; Calcium Channels; Centrifugation, Density Gradient; Cholic Acids; Chromatography, Gel; Deuterium; Deuterium Oxide; Digitonin; Male; Molecular Weight; Myocardium; Octoxynol; Polyethylene Glycols; Polysorbates; Rats; Rats, Inbred Strains; Receptors, Nicotinic; Solubility; Water

Rat brain opioid receptors were solubilized with digitonin and a zwitterionic detergent, 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS). The yield of solubilization was 70-75% with digitonin and 30-35% with CHAPS. Kinetic and equilibrium studies performed from digitonin extracts resulted in KD values comparable with those of the membrane fractions. Two [3H]naloxone binding sites were obtained in the extracts similarly to membrane fractions. The rank order potency of drugs used in the competition experiments did not change during solubilization. The distributions of mu, delta, and kappa opioid receptor binding sites were similar in membrane and digitonin-solubilized fractions (48-50% mu, 35-37% kappa, and 13-17% delta subtypes). The hydrodynamic properties of digitonin- and CHAPS-solubilized preparations were studied by sucrose density gradient centrifugation and Sepharose-6B chromatography. In all cases, two receptor populations were identified with the following parameters: sedimentation coefficients for the digitonin extracts were 9.2S and 13.2S and for CHAPS extract 8S and 15.6S; the Stokes radii were 45 A and 65A for the digitonin extract and 31A and 76A for the CHAPS-solubilized preparation.

Topics: Animals; Binding, Competitive; Brain; Brain Chemistry; Cell Membrane; Centrifugation, Density Gradient; Chemical Phenomena; Chemistry, Physical; Cholic Acids; Chromatography, Gel; Digitonin; Indicators and Reagents; Kinetics; Naloxone; Rats; Receptors, Opioid; Solubility

The three known visual pigments (P520, P450, P357) of the moth, Manduca sexta (Lepidoptera, Sphingidae), were extracted in two different detergents (2% digitonin, 6 or 12 mM CHAPS). As is the case in unextracted membranes, the metarhodopsins are quite stable in CHAPS extracts, while in digitonin the metarhodopsins of P520 and P450 decay rapidly at 15 degrees C to opsin and free retinal. The relative absorbance ratios are: 1.0:1.6 (P520:M485), 1.0:1.1 (P450:M485), and 1.0:0.8 (P357:M470). The relative amounts of the visual pigments found in digitonin extracts is 100:25:8 (P520:P450:P357); about 60 picomoles of P520 can be extracted from one Manduca retina.

Topics: Animals; Cholic Acids; Detergents; Digitonin; Female; Kinetics; Lepidoptera; Light; Male; Moths; Retinal Pigments; Retinaldehyde; Solutions; Spectrophotometry; Surface-Active Agents

This study describes a new method of solubilizing thyroid peroxidase (TPO) and partial purification of TPO from a small surgical specimen of human thyroid tissue. Graves' thyroid tissue was homogenized and centrifuged to obtain the 100 000 X g pellet. To solubilize TPO from the 100 000 X g pellet protein, the following four detergents were used: Triton X-100, digitonin, sodium deoxycholate, and 3-[(3-choramidpropyl)-dimethylammonio] 1-propanesulfate (CHAPS). For some samples, two detergents were combined and trypsin was also used. The best solubilization of TPO activity was obtained from the combination of digitonin-CHAPS-trypsin treatment or deoxycholate-CHAPS-trypsin treatment. The solubilized crude TPO was then chromatographed on a Sephacryl S 300 column. The results of chromatography indicated that detergent treatment alone did not separate TPO from other membrane proteins and the addition of trypsin was required for separation of TPO. Sephacryl chromatography of detergent-trypsin solubilized TPO was suitable as an initial step for purification of TPO from a small human thyroid tissue.

Topics: Cholic Acids; Deoxycholic Acid; Digitonin; Drug Stability; Graves Disease; Humans; Iodide Peroxidase; Octoxynol; Polyethylene Glycols; Solubility; Thyroid Gland; Trypsin

Previous studies have described the conversion, after detergent solubilization, of the multiple populations of membrane-bound muscarinic agonist binding sites to a population of uniform affinity. This paper describes the solubilization of at least two receptor species, distinct in their agonist binding characteristics, which are capable of interconversion by transition metal ions. This finding enabled a more detailed examination of the molecular properties and regional differences of brain muscarinic receptors than was previously possible. Muscarinic receptors (mAChR) obtained from the rat cerebral cortex or medulla pons were solubilized using digitonin or the zwitterion detergent, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (Chaps). The equilibrium binding of the antagonist [3H]-4-N-methylpiperidyl benzilate ([3H]4NMPB) to detergent-solubilized receptors resembled binding to neural membranes and exhibited subnanomolar affinity, saturability, and simple mass action kinetics. Agonist binding to soluble preparations was measured by competition of [3H]4NMPB binding sites. Saturation isotherms for agonist binding to digitonin- and Chaps-solubilized mAChR obtained from various brain regions appear flattened and have Hill coefficients in the range 0.52-0.78. Computerized modelling techniques indicate that the best fit to the experimental data is provided by a model specifying two soluble muscarinic agonist binding sites with differing dissociation constants, KH and KL, respectively. Solubilization of cerebral cortex membranes with Chaps or digitonin resulted in a population with a composition of high- and low-affinity sites similar to that found in the membrane-bound state. In contrast, solubilization of the medulla pons resulted in an approximately 40% loss of high-affinity sites. Solubilized receptors retained the sensitivity to transition metals ions, but were insensitive to guanine nucleotides. Density gradient centrifugation indicated that Chaps-solubilized mAChR are composed of two molecular forms with S20,W equal to 9.9 S and 14.9 S. The 14.9 S species comprises approximately 30% of the total binding activity in the cortex and approximately 40% in the medulla. We identify the 14.9 S species as being associated with a guanylnucleotide binding protein because treatment of medulla membranes with guanylylimidodiphosphate prior to solubilization results in disappearance of 14.9 S with 9.9 S unchanged. Sedimentation of cortical mAChR in the prese

Topics: Animals; Centrifugation, Density Gradient; Cerebral Cortex; Cholic Acids; Chromatography, Gel; Detergents; Digitonin; Guanine Nucleotides; Male; Mathematics; Medulla Oblongata; Metals; Models, Biological; Molecular Weight; Pons; Protein Conformation; Rats; Receptors, Muscarinic; Solubility

A series of detergents of varying chemical properties has been tested for solubilisation of bovine caudate nucleus D2 dopamine receptors using [3H]spiperone binding to assay the solubilised sites. The properties of the lysophosphatidylcholine (LPC)- and 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulphonate (CHAPS)-solubilised preparations are described in detail. The preparations are truly solubilised, and sucrose density gradient and gel filtration data are reported. Specific [3H]spiperone binding in the LPC-solubilised preparation assayed at 4 degrees C is solely to D2 dopamine receptors. If the assay temperature is raised to 25 degrees C, the amount of specific [3H]spiperone binding is largely unchanged, but it forms a greater proportion of the total [3H]spiperone binding owing to a reduction in nonstereospecific (spirodecanone) [3H]spiperone binding at the higher temperature. The effect of raising the assay temperature is important as it enables more precise determinations of specific [3H]spiperone binding to be made. Part of the specific [3H]spiperone binding at 25 degrees C is to solubilised S2 serotonin receptors in addition to D2 dopamine receptors. Good correlations are observed between the affinities for binding of ligands to the solubilised D2 receptors and corresponding data obtained on membrane-bound receptors. Agonist binding in LPC-solubilised preparations is insensitive to guanine nucleotides. It is speculated that the spirodecanone sites represent, in part, proteolysed or damaged D2 dopamine, or S2 serotonin, receptors. In the CHAPS-solubilised preparation the pharmacological profile of [3H]spiperone binding is unclear when assayed at 4 degrees C, but in assays at 25 degrees C a clear serotonin S2 receptor component of specific [3H]spiperone binding can be discerned.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Cattle; Caudate Nucleus; Centrifugation, Density Gradient; Cholic Acid; Cholic Acids; Detergents; Digitonin; Guanine Nucleotides; Lysophosphatidylcholines; Protease Inhibitors; Receptors, Dopamine; Sodium Chloride; Solubility; Spiperone; Surface-Active Agents

Picosecond transient absorption spectra of rhodopsin and isorhodopsin were measured at room temperature with a double-beam laser spectrophotometer after excitation at 355 nm. Photolysis studies were performed on rhodopsin solubilized in two different detergents (digitonin and 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate). The resulting rhodopsin/bathorhodopsin absorption difference spectra were measured at times from 35 ps to 250 ns following photoexcitation. Rhodopsin and isorhodopsin in native disk membrane were studied after suspension in 75% glycerol. Isorhodopsin was prepared by photoisomerizing rhodopsin in disk membrane at 77 K. Transient spectra obtained from the visual pigments in native membrane were of a quality approaching that obtained from detergent-solubilized rhodopsin. The batho intermediate derived from isorhodopsin was spectrally the same as that generated by rhodopsin photolysis and was produced with a quantum yield higher than had been predicted on the basis of other studies.

Topics: Animals; Cattle; Cell Membrane; Cholic Acids; Digitonin; Isomerism; Light; Photolysis; Retinal Pigments; Rhodopsin; Rod Cell Outer Segment; Solubility; Spectrophotometry

Various procedures for the solubilization of the imipramine-binding protein (IBP) of human platelets were compared. An IBP of a molecular weight of 300 000-400 000, as determined by exclusion chromatography on Sepharose 6B, was obtained with high amounts of digitonin and with lysolecithin. With smaller amounts of digitonin the molecular weight varied between more than 1 million and about 550 000 depending on the batch of detergent. The KD values and the IC50 values of drugs inhibiting imipramine binding were similar in the soluble preparation and in intact membranes. CHAPS and CHAPSO, even in high amounts, yielded solubilized IBP of high molecular weight (greater than 1 million). Membrane preparations of human platelets solubilized with high amounts of digitonin and with lysolecithin would therefore seem to be the most suitable for further purification of IBP.

Topics: Blood Platelets; Carrier Proteins; Cholic Acids; Detergents; Digitonin; Humans; Imipramine; Lysophosphatidylcholines; Membrane Proteins; Molecular Weight; Solubility

Topics: Animals; Cattle; Cholic Acids; Circular Dichroism; Detergents; Digitonin; Retinal Pigments; Rhodopsin; Spectrophotometry; Surface-Active Agents