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At least 883 records · Page 49Linked to original sources
PubMed1987

Dithiols and monothiols are linked with GABA transport in membrane vesicles of rat brain synaptosomes.

The properties of gamma-aminobutyric acid (GABA) transport into membrane vesicles derived from synaptosomes of rat brain have been studied using membrane-permeable and -impermeable sulfhydryl reagents, dithiol-specific reagents and oxidizing reagents. GABA transport is inhibited, reversibly, by very low concentrations of the membrane-permeable trivalent arsenical, phenylarsine oxide. Preincubation with this reagent only partially protects GABA transport from inactivation by N-ethylmaleimide (NEM). Thorin, a negatively charged trivalent arsenical, has no influence on GABA transport at concentrations 100-fold higher than that of the inhibitory phenylarsine oxide. The impermeant oxidizing agent, potassium ferricyanide, did not inhibit transport whereas the permeant reagent, diamide, was inhibitory. These data indicate that the GABA transporter possesses an activity-linked dithiol in a hydrophobic region of the carrier not accessible to charged, polar reagents. p-Chloromercuribenzenesulfonate (PCMBS) also inhibits but does not protect against NEM inactivation, suggesting the occurrence of an activity-linked monothiol in a polar region of the carrier.

Animals↗
PubMed1987

Sulfhydryl groups are involved in H+ translocation via the uncoupling protein of brown adipose tissue mitochondria.

Mersalyl inhibits H+ transport via the uncoupling protein (UP) in brown adipose tissue (BAT) mitochondria estimated as swelling in potassium acetate (Ki 67 microM) or as valinomycin-induced H+ extrusion in K2SO4 (Ki 55 microM) and KCl. The swelling in KCl is depressed only slightly. Some other SH-reagents (p-hydroxymercuribenzoate, 5,5'-dithiobis(2-nitrobenzoate) and thiolyte DB), but not hydrophobic reagents (N-ethylmaleimide and eosin-5-maleimide), exhibit analogous inhibition. Thus an essential SH-group localized at the water-accessible cytosolic surface of UP was found to be involved in H+ transport via UP but not in Cl- transport.

Adipose Tissue, Brown↗
PubMed1989

New chloride-activated aminopeptidase from human erythrocytes.

A new Cl- -activated aminopeptidase was purified from the cytosol of human erythrocytes as a single chain protein of an approx. Mr of 70,000 and pI of 5.1. The enzyme hydrolysed 2-naphthylamides of aliphatic, aromatic and basic L-amino acids, with a preference for the alanyl residue. It also hydrolysed di-, tri-, and some hydrophobic tetrapeptides. The inhibitors were bestatin, amastatin, Co2+, Zn2+, Mn2+, 4-hydroxymercuribenzoate and 1,10-phenanthroline. The activity of the enzyme, inhibited by 4-hydroxymercuribenzoate, was partially restored by the addition of sulfhydryl compounds. The presence of 0.2 M Cl- (Br-,F-) caused a several-fold increase in the isolated aminopeptidase activity.

Aminopeptidases↗
PubMed1991

Endothelium-derived relaxing factor is a nitrosyl iron complex with thiol ligands.

A hypothesis is put forward on the nature of the endothelium-derived relaxing factor (EDRF) which is released from vascular endothelial cells by acetylcholine, bradykinin and other agonists. It is suggested that EDRF is a nitrosyl iron complex with low-molecular thiol ligands, most probably with cysteine. Its active principle is nitric oxide (NO). This free radical is stabilized by inclusion into the iron complex, which promotes NO transfer within the cell and between cells. Subsequent release of NO from these complexes results from thiol group oxidation.

Acetylcholine↗
PubMed1993

Endothelin-receptor interactions. Role of a putative sulfhydryl on the endothelin receptor.

The mechanism of action of endothelin-receptor interactions was studied, using radioligand binding assays and SDS-PAGE, to investigate the possibility of disulfide interchange. Electrophoretic analysis suggested involvement of disulfide bond(s) in the receptor-ligand complex. Treatment of Et receptors with sulfhydryl-specific alkylating reagents (NEM or others) resulted in decreased ability to bind [125I]Et-1. [Dpr1-Asp15]Et-1, an antagonist homologous to Et but with an amide link replacing one of the disulfides, bound to Et receptors reversibly, but binding of Et-1 was less reversible. Preincubation of receptors with Et-1, but not with [Dpr1-Asp15]Et-1, protected receptors from alkylation with [14C]NEM. The data suggest that the Et receptor has a sulfhydryl group at or near the Et binding site. A model is proposed in which the role of the putative sulfhydryl group is discussed.

Animals↗
PubMed1994

Analysis of RNase A refolding intermediates by electrospray/mass spectrometry.

Electrospray/mass spectrometry (ES/MS) was extensively used to obtain information on disulphide-containing intermediates formed during refolding of bovine pancreatic ribonuclease A. The analysis showed the existence of an equilibrated population of disulphide bonded intermediates, and indicates that intermediates containing two intramolecular S-S are predominant until late stages of the refolding process. Mixed disulphides with exogenous glutathione were also detected, supporting previous evidence of conformational restrictions on the ability of RNase A to form intramolecular disulphides. The results indicate that ES/MS is a suitable technique to detect and characterize refolding intermediates.

Animals↗
PubMed1996

Transacylase-like structure and its role in substrate channeling of 6-hydroxymellein synthase, a multifunctional polyketide biosynthetic enzyme in carrot cell extracts.

6-Hydroxymellein synthase, a multifunctional polyketide biosynthetic enzyme of carrot, lost the binding ability toward its co-substrates, acetyl- and malonyl-CoAs, by the treatment with the blocking reagents for serine-OH. In contrast, the enzyme retained the binding ability even when the two SH groups at the reaction center (cysteine-SH of the condensation enzyme and cysteamine-SH of acyl carrier protein) were blocked, and one substrate bound to the SH-blocked enzyme was readily replaced by the other. It appeared that the cysteine-SH accepted only acetyl moiety while cysteamine-SH was preferentially malonylated in the presence of both of the substrates. These results suggest that transacylase-like domain is involved in the structure of 6-hydroxymellein synthase as a common primary binding site of its co-substrates, and acetyl and malonyl moieties are properly channeled from their CoA esters to cysteine-SH and acyl carrier protein-SH via this domain, respectively.

Acetyl Coenzyme A↗
PubMed1984

Human GMP synthetase.

The specific activity of GMP synthetase was measured in several human tissues and found to be highest in cultured skin fibroblasts, followed by bone marrow, leukocytes, erythrocytes, placenta, and liver. The enzyme from fibroblasts was purified approximately 50-fold by ammonium sulfate fractionation and gel filtration. The Km values were determined to be 4.9 microM for XMP, 270 microM for ATP, and 340 microM for glutamine. Ammonium sulfate could replace glutamine as the amino donor but was much less efficient. The enzyme was specific for ATP as the energy source. Unlike the calf thymus enzyme, the human enzyme has no requirement for a reduced sulfhydryl compound. Human GMP synthetase is inhibited by ATP, dATP, azaserine, and hydroxylamine.

Carbon-Nitrogen Ligases↗
PubMed1993

Purification and some properties of apurinic/apyrimidinic DNA endonucleases in rat liver.

1. Three kinds of apurinic/apyrimidinic (AP) DNA endonucleases, APcI, APcII, APcIII were purified from rat liver chromatin. 2. Molecular weights of APcI, APcII and APcIII were 30,000, 42,000 and 13,000 Da, which have isoelectric points of 7.2, 6.3 and 6.2, respectively. 3. Mg2+ was essential for the activities of these 3 enzymes, and sulfhydryl compounds (beta-mercaptoethanol) had a stimulatory effect on the enzyme activities while N-ethylmaleimide and HgCl2 inhibited the enzyme activity. 4. Km values of APcI, APcII and APcIII for AP site of DNA were 0.53, 0.27 and 0.36 microM, respectively, and AMP was the most potent inhibitor to these three enzymes among nucleotides tested.

Animals↗
PubMed1992

Kinetic behaviour and properties of aldehyde dehydrogenase from rat testis mitochondria. Effect of Mg2+ ions.

1. Mitochondrial aldehyde dehydrogenase is purified to near homogeneity by hydroxylapatite-, affinity- and hydrophobic interaction-chromatography. 2. The enzyme is an oligomeric protein and its molecular weight, as determined by gel-filtration, is 117,000 +/- 5000. 3. Active only in the presence of exogenous sulfhydryl compounds and NAD(+)-dependent, aldehyde dehydrogenase works optimally with linear-chain aliphatic aldehydes and is practically inactive with benzaldehyde. The pH-optimum is at about pH 8.5. 4. Km-Values for aliphatic aldehydes (C2-C6) range between 0.17 and 0.32 microM. The Km for NAD+ increases from 16 microM with acetaldehyde to 71 microM with capronaldehyde. 5. Millimolar concentrations of Mg2+ promote high increases of both V and Km for NAD+. At the same time, saturation curves with C4-C6 aldehydes can be simulated with a substrate inhibition model. 6. Inhibition by NADH is competitive: with capronaldehyde, the inhibition constant for NADH is 52 microM in the absence of Mg2+ and 14 microM in the presence of 4 mM Mg2+; with acetaldehyde, the inhibition constant is about three times higher (36 and 159 microM, respectively).

Aldehyde Dehydrogenase↗
PubMed1993

Inactivation of ornithine decarboxylase by intermediates of tyrosinase-catalyzed reaction.

1. Intermediates in the process of melanin synthesis formed through oxidation of catechols by tyrosinase produced the inactivation of ornithine decarboxylase (ODC), a key enzyme in the polyamine biosynthesis pathway. 2. The inactivation was dependent on the substrate used (dihydroxybenzylamine > L-3,4-dihydroxyphenylalanine > L-tyrosine) and on the concentration of intermediate produced rather than on the rate of formation. 3. Sulfhydryl compounds (dithiothreitol and glutathione) or quinone-reducing agents (ascorbic acid) prevented the inactivation of ODC; L-ornithine, but not other amino acids, also protected partially ODC. The results suggest that different cysteine residues in ODC molecule are implicated in the inactivatory event. 4. When 14C-labeled catechols were used, numerous polypeptides resulted labeled, showing that the reactive quinones formed as intermediates in the process of melanin biosynthesis bind covalently to many cellular proteins.

Animals↗
PubMed1994

Kinetics of manganese reconstitution and thiol group exposition in dialyzed rat mammary gland arginase.

1. Rat mammary gland arginase is a metallo-enzyme dependent on Mn2+, which can be only partially substituted by Cd2+. 2. Reconstitution of the activity of dialyzed arginase by manganese is a two-phase process; the second phase is independent of the cation concentration, with a half-time recovery (t1/2) of 10.77 min. 3. The apparent Km for Mn2+ is 280 microM and 10.5 microM for enzyme dialyzed for 24 and 72 hr, respectively. 4. Treatment with 5 mM EDTA at pH 6 totally inhibits enzyme activity, which is reconstituted by Mn2+. 5. Results obtained with iodoacetamide treatment suggest the existence of sulphydryl groups accessible only when the enzyme is dialyzed.

Animals↗
PubMed1982

Vitamin E dependent reduced glutathione inhibition of rat liver microsomal lipid peroxidation.

Effects of reduced glutathione (GSH) were investigated on in vitro lipid peroxidation of hepatic microsomes obtained from Long-Evans Hooded rats fed chemically defined, purified diets containing adequate or documented deficiencies of vitamin E (E), selenium (Se) or both. Glutathione inhibited lipid peroxidation mediated by both NADPH-dependent enzymatic and ascorbate-dependent non-enzymatic systems. The inhibitory effect of GSH was observed in microsomes obtained from E supplemented groups whereas it has no effect on microsomes from E deficient animals. Selenium status had no effect on GSH inhibition. Glutathione was found to be specific for the E dependent inhibition of lipid peroxidation and could not be substituted by other sulfhydryl compounds tested. Also, GSH did not inhibit non-enzymatic lipid peroxidation of heat-denatured microsomes from either E-supplemented groups or any of the other dietary regimens.

Animals↗