benzofurans and 7-chloro-4-nitrobenzofuran

A selective, sensitive, and precise HPLC method for the simultaneous determination of fluoxetine (FL) and its N-demethylated metabolite norfluoxetine (NFL) in human plasma has been developed. Following extraction with n-hexane, FL, NFL, and fluvoxamine (internal standard) were derivatized with 7-chloro-4-nitrobenzofurazan (NBD-Cl) under weakly alkaline conditions. NBD derivatives were extracted with chloroform after acidification and chromatographed on a reversed-phase column with gradient elution using acetonitrile and 0.1 mol/L nitric acid (pH 3) solution. Calibration curves were linear over the range of 1.0-100.0 ng/mL and 0.1-50.0 ng/mL for FL and NFL, respectively, with inter- and intraassay precision given by a relative standard deviation (RSD%) of less than 9.2%. The lower limits of quantification were 1.0 ng/mL for FL and 0.1 ng/mL for NFL. Recoveries of FL and NFL from plasma at three different concentrations were assessed. Average recovery was about 100% for both substances. The assay was applied to pharmacokinetic study in 2 healthy volunteers after a single oral administration of 40 mg of FL.

Topics: Administration, Oral; Area Under Curve; Benzofurans; Chromatography, High Pressure Liquid; Drug Administration Schedule; Drug Monitoring; Fluoxetine; Fluvoxamine; Half-Life; Hexanes; Humans; Kinetics; Reference Standards; Sensitivity and Specificity

Conversion of residue beta Tyr-297 of the Escherichia coli F1-ATPase (ECF1) to a Cys in the mutant beta Y297C led to impaired oxidative phosphorylation based on growth curves. The ATPase activity of ECF1 isolated from the mutant beta Y297C was only 1% of wild-type activity, but the residual activity involves cooperative multi-site enzyme turnover based on inhibition by DCCD and azide. ATPase activity could be increased to 8%, and 13% of wild-type by reaction of the introduced Cys with N-ethyl maleimide (NEM), and 7-chloro-4-nitrobenzofurazan (NbfCl), respectively, suggesting that enzymatic function is improved by an increased hydrophobicity of residue beta Cys-297. The mutation beta Tyr-297-->Cys had no effect on nucleotide binding in studies with the fluorescent analog lin-benzo-ADP. The asymmetry of ECF1 was investigated in the mutants beta Y297C and beta Y297C:E381C/epsilon S108C by examining the relative reactivity of Cys-297 in the three copies of the beta subunit under different nucleotide binding conditions. In agreement with a previous study (Haughton, M.A. and Capaldi, R.A. (1995) J. Biol. Chem., 270, 20568-20574), the asymmetry was maintained under all nucleotide conditions. The NbfCl reaction site was found to be beta free, which is also the site most reactive to NEM, beta epsilon is the second site which reacts with NbfCl or NEM, while the third site, beta gamma, is poorly reactive to either reagent.

Topics: Benzofurans; Binding Sites; Copper; Cross-Linking Reagents; Cysteine; Escherichia coli; Ethylmaleimide; Mutation; Nucleotides; Oxidative Phosphorylation; Protein Conformation; Proton-Translocating ATPases; Sulfhydryl Reagents

Inorganic pyrophosphatase (PPase) of S. cerevisiae is effectively inactivated by 7-chloro-4-nitrobenzofuran; the CaPP1 substrate analog has a protective effect. The modified enzyme separated from low molecular weight contaminants has an adsorption maximum at 345 nm. Preliminary modification of PPase SH-groups does not influence the enzyme binding to the inhibitor. The PPase activity is reconstituted by beta-mercapto-ethanol; hence, the inhibiting effect of the reagent is due to modification of tyrosine residues. A single reagent-containing peptide was isolated by specific adsorption from the tryptic hydrolysate of modified PPase. Within the primary structure of PPase, this peptide occupies positions 82-111 and contains two tyrosine residues. Hydrolysis of the isolated peptide by chymotrypsin and determination of the structure of fragments obtained by mass spectrometry and automated sequencing revealed that inactivation of PPase is due to selective modification of Tyr89.

Topics: Amino Acid Sequence; Benzofurans; Chromatography, Gel; Chromatography, High Pressure Liquid; Inorganic Pyrophosphatase; Mass Spectrometry; Mercaptoethanol; Molecular Sequence Data; Peptide Mapping; Pyrophosphatases; Saccharomyces cerevisiae; Tyrosine

Earlier it has been demonstrated that inactivation of inorganic pyrophosphatase (PPase) of S. cerevisiae by 7-chloro-4-nitronbenzofurasane is due to modification of Tyr89. The effect of pH and active center ligands on this reaction has been studied. It was found that pK for Tyr89 does not exceed 8.5; the phosphate-metal complex binding to the high affinity center protects Tyr89 from inactivation. Activating ions (Mg2+ and Zn2+) do not influence the inactivation, whereas the PPase inhibitor, Ca2+, enhances this process after saturation of the high affinity binding site. Saturation of two binding sites with Ca2+ has a protective effect on the enzyme. An increase in the rate of Tyr89 binding to the inhibitor in the presence of low concentrations of Ca2+ is due to the decrease of Tyr89 pK. The data obtained suggest that Tyr89 is located near the high affinity binding site for phosphate. The high reactivity of Tyr89 and its tight binding in the active center point to the presence of a hydrogen bondage with the substrate and suggest a role of a proton donor whose acceptor is the product of the enzymatic reaction, i.e., phosphate.

Topics: Benzofurans; Binding Sites; Calcium; Cations, Divalent; Inorganic Pyrophosphatase; Phosphates; Pyrophosphatases; Saccharomyces cerevisiae; Tyrosine

A 30-year-old pharmacist suffered from acute allergic contact dermatitis due to 4-chloro-7-nitrobenzofurazan (NBD-Cl). Contact allergy towards this reagent and 2 of its reaction products was proven by patch tests. As NBD-Cl has not been reported as an allergen before, the characteristics of this chemical and its use as an analytical reagent are briefly surveyed. Similarities to dinitrochlorobenzene (DNCB) are pointed out.

Topics: Acute Disease; Adult; Benzofurans; Dermatitis, Contact; Dermatitis, Occupational; Female; Humans; Praziquantel

The catalytically active alpha 3 beta 3 complex, assembled as described (Miwa, K., and Yoshida, M. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 6484-6487) from the isolated alpha and beta subunits of the F1-ATPase of the thermophilic bacterium PS3 (TF1), is inactivated by 7-chloro-4-nitrobenzofurazan (Nbf-Cl) with characteristics very similar to those observed when TF1, which has the subunit composition, alpha 3 beta 3 gamma delta epsilon, is inactivated by the reagent under the same conditions. Both native TF1 and the alpha 3 beta 3 complex are inactivated by 200 microM Nbf-Cl with a pseudo-first order rate constant of 3.7 x 10(-2) min-1 in the presence of 0.2 M Na2SO4 at pH 7.6 and 23 degrees C. The rate of increase in absorbance at 385 nm of reaction mixtures containing 200 microM [14C]Nbf-Cl and TF1, the wild-type alpha 3 beta 3 complex, or the mutant alpha 3(beta Y307----F)3 complex, each at 18 microM was also examined. Since the alpha 3(beta y307----F)3 complex is resistant to inactivation by Nbf-Cl, difference spectrophotometry revealed that inactivation of native TF1 and the wild-type alpha 3 beta 3 complex could be correlated with formation of about 1 mol of Nbf-O-Tyr/mol of enzyme or complex. Fractionation of peptic digests of the labeled enzyme and complexes by reversed-phase high performance liquid chromatography resolved a major radioactive peptide that was common to labeled TF1 and the labeled alpha 3 beta 3 complex but was absent in the digest of the labeled alpha 3(beta Y307----F)3 complex. This labeled peptide was shown to contain Tyr-beta 307 derivatized with [14C]Nbf-Cl by automatic amino acid sequence analyses. From these results, it is concluded that one-third of the sites' reactivity of Nbf-Cl with Tyr-beta 307 in TF1 or its equivalent in other F1-ATPases is not influenced by the presence of the gamma, delta, or epsilon subunits. It has also been shown that Tyr-307 is not modified to an appreciable extent when the isolated beta subunit is treated with [14C]Nbf-Cl under conditions in which this residue is nearly completely labeled in a single beta subunit when TF1 or the alpha 3 beta 3 complex is inactivated by the reagent.

Topics: Bacteria; Benzofurans; Kinetics; Macromolecular Substances; Mutation; Peptide Fragments; Proton-Translocating ATPases; Tyrosine

7-Chloro-4-nitrobenzofurazan (NBD-Cl) is a potent inhibitor of both types of monoamine oxidase (MAO). NBD-Cl competitively inhibited the oxidative deamination of kynuramine catalyzed by human placenta MAO-A, the oxidative deamination of benzylamine catalyzed by bovine liver MAO-B, the oxidative deamination of serotonin catalyzed by rat brain MAO-A, and the oxidative deamination of phenylethylamine catalyzed by rat brain MAO-B. In addition, a time-dependent inactivation of MAOs by NBD-Cl has been demonstrated upon incubation of the enzyme preparations with NBD-Cl at pH 9, but not at pH 7.5. The time-dependent inhibition of MAO by NBD-Cl could be prevented by the addition of 4-nitrophenyl azide, an active site-directed label of MAO, during incubation of the enzyme with NBD-Cl. On the basis of these findings, it is suggested that at pH 9, NBD-Cl modifies one (or more) essential lysine residue(s) in the active sites of the two types of MAO.

Topics: Animals; Benzofurans; Binding, Competitive; Brain; Cattle; Female; Hydrogen-Ion Concentration; Kinetics; Mitochondria; Mitochondria, Liver; Monoamine Oxidase Inhibitors; Placenta; Pregnancy; Rats

(1) The hydrolytic activity of the isolated mitochondrial ATPase (F1) is strongly inhibited by azide. However, at very low ATP concentration (1 microM or less), no inhibition by azide is observed. (2) The azide-insensitive ATPase activity represents a high-affinity, low-capacity mode of turnover of F1. This is identified with the low Km, low Vmax component seen in steady-state kinetic studies in the absence of azide. (3) The azide-insensitive ATPase activity shows simple Michaelis-Menten kinetics, with Km = 3.2 microM, and Vmax = 1.1 mumol/min per mg (6 s-1). It is unaffected by anions such as sulphite, or by increasing pH in the range 7 to 8, both of which stimulate the maximal activity of F1. (4) Both the azide-insensitive and azide-sensitive components of F1-ATPase activity are equally inhibited by labelling the enzyme with 7-chloro-4-nitrobenzofurazan, by binding the natural inhibitor protein, or by cold denaturation of the enzyme. (5) It is concluded that azide-insensitive ATP hydrolysis represents catalysis by F1 involving a single catalytic site, and that azide acts by abolishing intersubunit cooperativity between the three catalytic sites of F1. Azide-sensitivity is thus a useful probe for events which affect the active site of F1 directly.

Topics: Adenosine Triphosphate; Animals; Anions; Azides; Benzofurans; Binding Sites; Cattle; Hydrogen-Ion Concentration; Hydrolysis; Inosine Triphosphate; Kinetics; Mitochondria, Heart; Proton-Translocating ATPases; Sulfites

The characteristics and specificity of inactivation of the chloroplast F1-ATPase (CF1) with 7-chloro-4-nitrobenzofurazan (Nbf-Cl) have been investigated. Inactivation of the octylglucoside-dependent Mg2+-ATPase activity of latent CF1 by Nbf-Cl can be correlated with the formation of about 1.2 mol of Nbf-O-Tyr per mole of enzyme. Following inactivation of CF1 with [14C]Nbf-Cl, polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate revealed that the majority of the radioactive reagent incorporated is present in the beta subunit. Treatment of the enzyme with [14C]Nbf-Cl following dithiothreitol heat activation, led to similar labeling of the beta subunit and substantial incorporation of 14C into the gamma subunit. On complete inactivation, about 4 mol of Nbf-S-Cys is formed per mole of dithiothreitol-heat-activated CF1. Incorporation of 14C into the gamma subunit is prevented by prior treatment of the latent CF1 or of the dithiothreitol-heat-activated CF1 with iodoacetamide. Following incubation of the dithiothreitol-heat-activated CF1 with iodoacetamide, complete inactivation of the octylglucoside-dependent Mg2+-ATPase activity by Nbf-Cl can be correlated with the formation of about 1.2 mol of Nbf-O-Tyr per mole of enzyme. After stabilization of the [14C]Nbf-O-Tyr derivative by treatment with sodium dithionite, a labeled peptide was purified. Automatic Edman degradation of this peptide revealed the sequence V-X-V-P-A-D-(D). The majority of the radioactivity was cleaved in the second cycle, the position occupied in CF1 by Tyr-beta-328, which is homologous to Tyr-beta-311, the residue reactive with Nbf-Cl in the beef heart mitochondrial F1-ATPase. When CF1, modified at Tyr-beta-328 with Nbf-Cl, is incubated at pH 9.0, the Nbf-O-Tyr adduct is hydrolyzed, leading to concomitant recovery of the ATPase activity. In double labeling experiments, two-dimensional isoelectric focusing in the presence of urea followed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate indicates that 2-azido-ADP, covalently bound at the tight ADP binding site, and the tyrosine modified by [14C]Nbf-Cl are located in different beta subunits.

Topics: Benzofurans; Ca(2+) Mg(2+)-ATPase; Calcium-Transporting ATPases; Chloroplasts; Electrophoresis, Polyacrylamide Gel; GTP Phosphohydrolases; Macromolecular Substances; Plants; Proton-Translocating ATPases; Spectrum Analysis; Structure-Activity Relationship

The characteristics of ATP hydrolysis at a single catalytic site of the bovine heart F1-ATPase (MF1) as originally described by Grubmeyer et al. (Grubmeyer, C., Cross, R.L., and Penefsky, H.S. (1982) J. Biol. Chem. 257, 12092-12100) were compared with those of various chemically modified preparations of MF1 in which the steady state activity was severely attenuated. Although it was not necessary to age our preparations of native MF1 in the presence of 2 mM Pi to observe the same characteristics of single site catalysis, such aging did shift the equilibrium of bound substrate and bound products at the single catalytic site in favor of ATP. After loading a single catalytic site on the enzyme with substoichiometric [alpha,gamma-32P]ATP, the addition of 5-20 microM ATP or ADP was effective in promoting both the hydrolysis of bound [alpha,gamma-32P]ATP and release of radioactive products. Under these conditions, the 5-20 microM ATP added as promoter was hydrolyzed at a rate commensurate with the turnover rate of the enzyme, whereas the promoted hydrolysis of the [alpha,gamma-32P]ATP, preloaded at a single catalytic site, was considerably slower. Therefore, the high affinity, single catalytic site loaded first does not directly contribute to steady state ATP hydrolysis. That the single, high affinity catalytic site is not a "normal" catalytic site is supported by the properties of enzyme modified by 5'-p-fluorosulfonylbenzoyladenosine which exhibits only slightly altered characteristics of single site catalysis and promoted single site catalysis, despite exhibiting severely attenuated steady state turnover. Other modified forms of the enzyme in which the steady state activity was severely attenuated by derivatization with 5'-p-fluorosulfonylbenzoylinosine, 7-chloro-4-nitrobenzofurazan, or 1,5-difluoro-2,4-dinitrobenzene also bound substoichiometric ATP at a single catalytic site. However, the characteristics of single site hydrolysis by these modified forms of the enzyme differed considerably from those of native MF1.

Topics: Adenosine; Adenosine Triphosphate; Affinity Labels; Animals; Benzofurans; Binding Sites; Cattle; Dinitrofluorobenzene; Hydrolysis; Inosine; Mitochondria, Heart; Proton-Translocating ATPases; Structure-Activity Relationship

Two classes of ADP binding sites at 20 degrees C have been characterized in the F1-ATPase from the thermophilic bacterium, PS3 (TF1). One class is comprised of three sites which saturate with [3H]ADP in less than 10 s with a Kd of 10 microM which, once filled, exchange rapidly with medium ADP. The binding of ADP to these sites is dependent on Mg2+. [3H]ADP bound to these sites is removed by repeated gel filtrations on centrifuge columns equilibrated with ADP free medium. The other class is comprised of a single site which saturates with [3H]ADP in 30 min with a Kd of 30 microM. [3H]ADP bound to this site does not exchange with medium ADP nor does it dissociate on gel filtration through centrifuge columns equilibrated with ADP free medium. Binding of [3H]ADP to this site is weaker in the presence of Mg2+ where the Kd for ADP is about 100 microM. [3H]ADP dissociated from this site when ATP plus Mg2+ was added to the complex while it remained bound in the presence of ATP alone or in the presence of ADP, Pi, or ADP plus Pi with or without added Mg2+. Significant amounts of ADP in the 1:1 TF1.ADP complex were converted to ATP in the presence of Pi, Mg2+, and 50% dimethyl sulfoxide. Enzyme-bound ATP synthesis was abolished by chemical modification of a specific glutamic acid residue by dicyclohexylcarbodiimide, but not by modification of a specific tyrosine residue with 7-chloro-4-nitrobenzofurazan. Difference circular dichroism spectra revealed that the three Mg2+ -dependent, high affinity ADP binding sites that were not stable to gel filtration were on the alpha subunits and that the single ADP binding site that was stable to gel filtration was on one of the three beta subunits. It has also been demonstrated that enzyme-bound ATP is formed when the TF0.F1 complex containing bound ADP was incubated with Pi, Mg2+, and 50% dimethyl sulfoxide.

Topics: Adenosine Diphosphate; Bacteria; Benzofurans; Binding Sites; Circular Dichroism; Hot Temperature; Kinetics; Magnesium; Protein Binding; Protein Conformation; Proton-Translocating ATPases; Quinacrine Mustard; Tritium; Tyrosine

Topics: Amino Acids; Animals; Aorta, Thoracic; Benzofurans; Chromatography, High Pressure Liquid; Collagen; Hydrolysis; Indicators and Reagents; Kinetics; Male; Neoplasms, Experimental; Rats; Rats, Inbred Strains

When bovine heart mitochondrial F1-ATPase, taken as alpha 3 beta 3 gamma delta epsilon with a molecular weight of 375,000, was inactivated by greater than 90% with a 4-fold molar excess of 7-chloro-4-nitro[14C]benzofurazan at pH 7.4, 1.15 mol of 4-nitrobenzofurazan [14C]Nbf were incorporated per mol of enzyme. Reactivation of a sample of the modified enzyme with dithiothreitol removed 0.82 mol of [14C]Nbf/mol of the F1-ATPase indicating that, of the 1.15 mol of [14C]Nbf incorporated, 0.82 mol were present on tyrosine residues and 0.33 mol on lysine residues. Incubation of the modified enzyme at pH 9.0 for 18 h at 23 degrees C led to an increase of 0.64 mol of [14C]Nbf-N'-Lys/mol of the F1-ATPase which occurred as a consequence of an O----N migration. About 15% enzyme reactivation occurred simultaneously with the migration indicating that the fraction of the [14C]Nbf group originally present on tyrosine which did not migrate was lost by hydrolysis. Examination of a tryptic digest of the labeled enzyme after the O----N migration by reversed-phase high-pressure liquid chromatography revealed a single major radioactive peptide. The labeled tryptic fragment was purified and subjected to automatic Edman degradation. This analysis revealed that Lys-beta-162 was specifically labeled during the O----N migration of the [14C]Nbf group.

Topics: Amino Acids; Animals; Benzofurans; Binding Sites; Carbon Radioisotopes; Cattle; Lysine; Mitochondria, Heart; Oxadiazoles; Peptide Fragments; Protein Binding; Proton-Translocating ATPases; Trypsin