sodium-dodecyl-sulfate and chapso

Wild-type and mutant forms of bacteriorhodopsin (sbR) from Halobacterium salinarium, produced by Escherichia coli overexpression of a synthetic gene, were reversibly unfolded in 1, 2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 3-[(3-cholamidopropyl)dimethylamino]-2-hydroxyl-1-propane (CHAPSO), and sodium dodecyl sulfate (SDS) mixed micelles. To study the effect on protein stability by substitutions on the hydrophobic surface with polar residues, the unfolding behavior of a G113Q, G116Q mutant [sbR(Q2)] was compared to the wild-type sbR [sbR(WT)]. sbR(Q2) was more sensitive to SDS-induced unfolding than sbR(WT) under equilibrium conditions, and kinetic experiments showed that sbR(Q2) was more sensitive to acid-induced denaturation and thermal unfolding than sbR(WT). Since the mutations in sbR(Q2) were on the detergent-embedded hydrophobic surface of sbR, protein destabilization by these mutations supports the concept that the membrane-embedded segments are important for the stability of sbR. Our experiments provide the basis for studying the thermodynamic stability of sbR by evaluating reversible folding and unfolding conditions in DMPC/CHAPSO/SDS mixed micelles.

Topics: Amino Acid Substitution; Bacteriorhodopsins; Cholic Acids; Detergents; Dimyristoylphosphatidylcholine; Guanidine; Halobacterium salinarum; Hydrogen-Ion Concentration; Micelles; Point Mutation; Protein Denaturation; Protein Folding; Recombinant Fusion Proteins; Sodium Dodecyl Sulfate; Solutions; Spectrophotometry, Ultraviolet; Temperature; Urea

Enhancement of the fluorescence intensity of colchicine occurs in media of low polarity and appreciable viscosity; this is suggested to be the basis of the intensification of its fluorescence when it is bound to and immobilized in tubulin. We show here that the tubulin-bound fluorescence features of colchicine are largely reconstructed upon solubilizing it in chosen micellar aggregates that offer optimal polarities and microviscosities. Triton X-100 and bile salt micelles intensify the colchicine emission but the maximal effects are obtained with tetrameric aggregates of the peptide melittin. Estimates of the polarity, microviscosity and binding-site dimensions of colchicine are obtained using this mimetic approach. Our results suggest that well chosen micellar systems act as good models to reconstruct and analyze the spectral properties of molecules immobilized in their binding sites.

Topics: Binding Sites; Cetrimonium; Cetrimonium Compounds; Cholic Acids; Colchicine; Colloids; Deoxycholic Acid; Dioctyl Sulfosuccinic Acid; Fluorescence; Fluorescence Polarization; Melitten; Micelles; Octoxynol; Polyethylene Glycols; Sodium Dodecyl Sulfate; Solubility; Surface-Active Agents; Tubulin; Viscosity

1. Renaturation of a 3'-nucleotidase from the surface membrane of Leishmania donovani promastigotes was achieved following polyacrylamide gel electrophoresis (PAGE) in the presence of sodium dodecyl sulfate (SDS). 2. Enzyme activity was detected in situ in gels, following SDS removal, by incubating the gels in reaction mixtures containing 3'-AMP or 3'-UMP as substrate followed by staining for the inorganic phosphate (Pi) reaction product with malachite green-molybic acid solution. 3. Conditions for the removal of SDS by diffusion and for the renaturation of enzyme activity are described including evidence for the detergent requirement, which is best satisfied by 3[(3-cholamidopropyl)-dimethylammonio]2-hydroxy-1-propane sulfonate (CHAPSO). 4. Results indicate that the 3'-nucleotidase migrates under these conditions as a polypeptide with an Mr of 43,000.

Topics: Animals; Cholic Acids; Detergents; Electrophoresis, Polyacrylamide Gel; Leishmania donovani; Molecular Weight; Nucleotidases; Sodium Dodecyl Sulfate; Substrate Specificity