Enoyl coenzyme A hydratase (crotonase). Enhancement of the rate of hydration of crotonylpantetheine by coenzyme A and related compounds.
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Acylation↗
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[Correlation between sulfhydryl groups of myosin and phosphorus compounds during decomposition of adenosintriphosphoric acid].
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Adenosine Triphosphate↗
Absorption of methylmercury compounds from rat intestine.
Intestinal absorption of methylmercury complexed with non-protein sulfhydryl compounds (NPSHs) as occurs in bile was studied by means of direct injection of mercury compounds into ligated intestinal segments of rats. The extent of absorption of methylmercury-cysteinylglycine (MM-CysGly) was similar to that of methylmercury-cysteine (MM-Cys) and 1.5 times larger than that of methylmercury-glutathione (MM-GSH). This results suggested that MM-CysGly, which is recognized as a major component of methylmercury in rat bile, can be easily reabsorbed from the intestine. These results indicate that not only MM-GSH and MM-Cys but also MM-CysGly may play important roles in the intestinal reabsorption of methylmercury during its enterohepatic circulation. When the ligated intestine was pretreated with probenecid and acivicin, the intestinal absorption of MM-GSH was depressed much more than in the case of treatment with acivicin alone. This indicates the possibility that there are at least two systems for intestinal transport of MM-GSH, i.e. gamma-glutamyltranspeptidase (GGT)-dependent and -independent systems.
Animals↗
Inhibition of polymorphonuclear leukocyte functions by fluorinated nitrobenzenes.
The bifunctional fluorinated nitrobenzenes, 1,5-difluoro-2,4-dinitrobenzene (DFDNB) and 4,4'-difluoro-3,3'-dinitrodiphenyl sulfone (DFDNDPS), and the monofunctional 1-fluoro-2,4-dinitrobenzene (FDNB) inhibit chemotaxis, phagocytosis, exocytosis and the respiratory burst of rabbit polymorphonuclear leukocytes. Inhibition occurs in the micromolar concentration range; the bifunctional compounds are stronger inhibitory than the monofunctional one. The inhibitory effect can be counteracted by sulfhydryl compounds and not with amino-group containing compounds. The results suggest that an interaction with vulnerable sulfhydryl groups, located in a hydrophobic surrounding, is the basis of the inhibitory effect of the fluorinated nitrobenzenes.
Animals↗
Cystinuria.
Cystinuria is an inherited metabolic disease resulting in renal stone formation. An incidence of 1 in 7000 makes it a relatively common genetic disease. The biochemical defect is a carrier protein in the epithelial cells of certain organs. This carrier protein is responsible for the transport of cystine and the dibasic amino acids. Cystine is a poorly soluble compound which precipitates in acid urine and results in renal calculi. Cystine stones account for 1 to 2% of all renal calculi. Homozygotes are detected by the high concentration of cystine in their urine. Treatment consists of sulfhydryl compounds that form more soluble compounds with cystine through sulfhydryl exchange as well as alkalinization of urine and hydration to make cystine more soluble.
Amino Acids↗
Thiol-mediated catalysis of nitroglycerin degradation by serum proteins. Increase in metabolism was not accompanied by S-nitrosothiol production.
In vitro degradation of nitroglycerin (NTG) in human plasma has been shown to be accelerated significantly by sulfhydryl compounds. The interaction between NTG and N-acetyl-1-cysteine (NAC) in human plasma produces a pharmacologically active S-nitrosothiol, which may be responsible, at least in part, for the in vivo nitrate tolerance-reversing effect of NAC. The mechanism of this thiol-mediated NTG degradation in plasma has not been identified. In this report, we examined the catalytic activity of various plasma proteins toward NAC-mediated NTG degradation and found human serum albumin (HSA) to have the highest catalytic activity among the proteins tested. However, the dinitrate metabolite distribution ratio found with HSA (favoring the 1,3- over the 1,2-isomer) was substantially different from that observed with human plasma (where equal amounts of both dinitrates were produced). In addition, the HSA-catalyzed degradation of NTG did not lead to enhanced formation of S-nitrosothiol. These findings therefore argue against a predominant role exerted by HSA in the thiol-mediated NTG metabolism in plasma. The HSA-mediated catalysis of NTG was partially blocked by pretreatment with NAC followed by a thiol-alkylating agent, suggesting that the catalytic mechanism was due, in part, to the conversion of disulfide linkages within the HSA structure to reactive sulfhydryl groups.
Acetylcysteine↗
Resting chondrocytes in culture survive without growth factors, but are sensitive to toxic oxygen metabolites.
Chondrocytes in dense suspension culture in agarose survive in serum-free DME because they secrete low molecular mass compounds supporting their own viability. This activity can be replaced by pyruvate, or sulfhydryl compounds, e.g., cysteine or dithioerythritol. Catalase, an enzyme decomposing H2O2, also protects the cells, whereas superoxide dismutase has no effect. Therefore, chondrocytes in culture are sensitive to toxic compounds derived from molecular oxygen, i.e., hydroxyl radicals or hydrogen peroxide spontaneously generated in DME containing ascorbate and ferrous ions. Poly-ADP-ribosylation is an important step in the cascade of events triggered by these compounds. To survive, chondrocytes do not require stimulation by growth factors. They remain resting cells in fully defined, serum-free culture also at low density. Proliferation and hypertrophy can be induced by serum, but not by low cell density alone.
Animals↗
Coupling of a proton pump with superoxide radical-superoxide dismutase system in maturing mammalian spermatozoa and its association with sperm motility.
Mammalian spermatozoa possess a membrane-located 'proton pump' which appears to regulate the acquisition and maintenance of their motility. The 'proton pump' seems to be coupled with the superoxide radical-superoxide dismutase system which, when uncoupled, results in total loss of sperm motility. Addition of sulfhydryl-compounds restarts the proton pump and reactivates sperm motility. Cobaltous ions block the membrane sulfhydryl groups and it is proposed that the sulfhydryl groups may be involved in regulating proton secretion and sperm motility.
Animals↗
Source of energy for gliding motility in Flexibacter polymorphus: effects of metabolic and respiratory inhibitors on gliding movement.
The effects of selected metabolic and respiratory inhibitors on the gliding motility of Flexibacter polymorphus were examined. Motility and oxygen consumption were quantitatively inhibited in a reversible manner by specific respiratory poisons, suggesting that gliding velocity was linked to electron transport activity. Arsenate had little influence on the number or rate of gliding filaments, despite a 95% decrease in the concentration of intracellular adenosine 5'-triphosphate (ATP). At concentrations of cyanide or azide that abolished gliding movement, cells possessed a level of ATP that should have been sufficient to allow motility. Proton-conducting uncouplers of oxidative phosphorylation, such as carbonylcyanide m-chlorophenylhydrazone (CCCP) and tetrachlorosalicylanilide, strongly inhibited locomotion yet did not suppress respiratory activity or intracellular ATP sufficiently to account for their effect on movement. Inhibition of motility by CCCP (but not by tetrachlorosalicylanilide) was partially reversed by sulfhydryl compounds. However, unlike CCCP, inhibition of motility by p-chloromercuribenzoate, a known sulfhydryl-blocking reagent, was associated with a corresponding reduction in respiratory activity and ATP content of cells. Protein synthesis was not blocked by concentrations of CCCP inhibitory for motility, indicating that utilization of existing ATP in this energy-requiring process was not impaired. These data suggest (but do not unequivocally prove) that ATP may not function as the sole energy donor for the gliding mechanism, but that some additional product of electron transport is required (e.g., the intermediate of oxidative phosphorylation).
Adenosine Triphosphate↗
Folic acid conjugase from Plasma. I. Partial purification and properties.
Human plasma conjugase was partially purified by ammonium sulphate and DEAE-cellulose column fractionation. The pH optimum was found to be 4.5. The enzyme followed normal Michaelis-Menten Kinetics. The Km value was found to be 1.4 x 10(-7)M for folylheptaglutatmate assuming this compound to be the predominant form of folate in yeast extract. The enzyme required sulfhydryl compounds for full activity. Differential microbiological assay of the conjugase reaction product using L. casei and S. faecalis as the test organisms revealed that during the initial stage of the reaction considerable portion of the reaction product was at polyglutamyl stage. On prolonged incubation polyglutamates decreased due to further hydrolysis of the gamma-glutamyl residues. The plasma conjugase activity of different species of animals showed wide variations. Goat, dog and rabbit plasma had neglibible activity while monkey, guinea pig and chick plasma had moderate activity. Bovine plasma had low activity while rat plasma had high activity. The plasma conjugase activity of normal Indian adults ranged from 400 to 900 units per ml, and there was no significant sex difference. The values obtained are considerably higher than those reported in literature.
Animals↗
Modulation of rabbit neutrophil chemotaxis by cytochalasin A. A comparison with other neutrophil functions.
Chemotaxis and stimulated locomotion by rabbit peritoneal neutrophils are inhibited by cytochalasin A; inhibition is complete with 5 X 10(-7) M cytochalasin A. Under the same conditions exocytosis and activation of the metabolic burst are stimulated maximally with 5 X 10(-7) M cytochalasin A. Inhibition of these function occurs at concentrations higher than 10(-6) M, inhibition being complete with 5 X 10(-6) M cytochalasin A. The sulfhydryl compound glutathione can prevent the inhibitory effect of cytochalasin A on chemotaxis. Inactivation of the sulfhydryl groups on the outer surface of the plasma membrane does not affect the inhibitory effect of cytochalasin A. It is concluded that the cellular target of cytochalasin A has a different significance for chemotaxis as compared with exocytosis and metabolic burst. The possibility that cytochalasin A reacts with sulfhydryl groups, located on a structure closely connected with the inner surface of the plasma membrane, is discussed.
Animals↗
[Effect of 3, 4-benzopyrene on the concentration of thiols in the tissues].
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Benz(a)Anthracenes↗
Fine stuctural alterations in cell particles during chemical carcinogenesis. II. Further evidence for their involvement in the mechanism of carcinogenesis. The swelling of rat liver mitochondria during feeding of amino azo dyes.
Swelling under carefully controlled conditions has been used to study alterations in the structure of rat liver mitochondria as a result of feeding azo dyes. The changes of the swelling properties of the mitochondria during feeding of the hepatocarcinogenic 3'-methyl-4-dimethylaminoazobenzene are essentially comparable to those observed previously with the microsomes, under the same dietary conditions. These alterations in mitochondrial swelling are not related to changes in the amount of these cell particulates per unit weight of tissue, during feeding of this azo dye. As with the microsomes, feeding of the isomeric but relatively noncarcinogenic 2-methyl-4-dimethylaminoazobenzene does not affect swelling. The structural differences between liver and hepatoma mitochondria show up not only in the rate and extent of swelling but also in the form of the curves of pH dependence. The influence of ketones and sulfhydryl compounds on the swelling of normal liver mitochondria were studied, with particular emphasis to the role of sulfhydryl groups in membrane permeability. The sudden steep rise in the tumor incidence in groups of rats fed 3'-methyl-4-dimethylaminoazobenzene for increasing intervals of time occurs at about 4 weeks. This time correlates with the point of the minimum swelling of microsomes and mitochondria isolated from the livers of rats fed this same dye. Thus, a correlation is established between the alterations of the swelling properties of these particulates and the carcinogenic process.
Animals↗
Light and stomatal metabolism : I. Possible involvement of light modulation of enzymes in stomatal movement.
New evidence is provided regarding the direct effect of light on stomatal opening in the epidermis of the pea (Pisum sativum L. var Little Marvel) leaf. Light modulates the activity of a number of key enzymes involved in stomatal metabolism. When isolated epidermal strips are illuminated, phosphoenolpyruvate carboxylase, NADP-malate dehydrogenase, and NADP-isocitrate dehydrogenase are activated; and aspartate aminotransferase is inactivated. Sulfhydryl compounds, dithiothreitol and glutathione, enhance stomatal opening in epidermal strips both in light or darkness while the sulfhydryl reagent N-ethylmaleimide inhibits, indicating the possible involvement of sulfhydryl groups in stomatal movements. Further, light treatment increases measureable thiol levels in the epidermis about 3-fold. These results suggest that light modulation of enzymes in the epidermis may play a significant role in the mechanism of stomatal movement.
Journal Article↗
Regulation of liver phosphorylase phosphatase by glutathione disulfide.
The mechanism of inactivation of rabbit liver phosphorylase phosphatase by glutathione disulfide (GSSG) was investigated. The catalytic subunit of phosphorylase phosphatase was inactivated by GSSG and other disulfides. Inactivation by GSSG was a concentration-dependent process and resulted in the formation of an inactive, stable enzyme species. The inactivated enzyme could be reactivated by addition of various sulfhydryl compounds, including glutathione (GSH). Homogeneous phosphorylase phosphatase contains, per mol of catalytic subunit (Mr = 33,000), two sulfhydryl groups, one of which reacted with GSSG to form inactive enzyme. Binding studies with [glycine-2-3H]GSSG revealed simultaneous incorporation of 3H radioactivity into the catalytic subunit and stoichiometric loss of catalytic activity. Treatment of the 3H-labeled enzyme with GSH was accompanied by release of 3H radioactivity from the enzyme and restoration of enzyme activity. The results suggest that inactivation of phosphorylase phosphatase by GSSG results from the formation of a mixed disulfide between GSSG and one of the two sulfhydryl groups in the catalytic subunit.
Animals↗
Metallothionein and glutathione as determinants of cellular retention and extrusion of cadmium and mercury.
This work explored cellular trapping and extrusion of Cd and Hg in epithelial cells, with special emphasis on the jejunal mucosa. Important determinants of these processes are the concentration, diffusibility and relative metal affinities of a variety of cellular metal-binding compounds including metallothionein (MT). As predicted from the known properties of MT, this protein can compete with other sulfhydryl compounds for Cd but not for Hg; this is illustrated by the observation that glutathione (GSH) stimulates extrusion of only Hg. Similar factors can help explain why, in spite of its tighter binding by MT, Hg has a shorter biological half-life in renal cortex than does Cd. Metal extrusion from cells presumably involves movement of diffusible complexes such as HgGSH.
Animals↗
Reversible, coenzyme-A-mediated inactivation of biosynthetic condensing enzymes in yeast: a possible regulatory mechanism.
alpha-Isopropylmalate synthase [3-hydroxy-4-methyl-3-carboxyvalerate 2-oxo-3-methylbutyrate-lyase (CoA-acetylating); EC 4.1.3.12], the enzyme catalyzing the first committed step in leucine biosynthesis, and homocitrate synthase [3-hydroxy-3-carboxyadipate 2-oxoglutarate-lyase (CoA-acetylating); EC 4.1.3.21], the first enzyme in lysine biosynthesis in yeast, are rapidly inactivated in the presence of low concentrations of coenzyme A, a product of both reactions. Closely related compounds like 3-dephospho-coenzyme A or oxidized coenzyme A are almost without effect, as are other sulfhydryl compounds. Citrate (si)-synthase [citrate oxaloacetate-lyase (pro-3S-CH2-COO-minus leads to acetyl-CoA); EC 4.1.3.7] appears to be completely resistant against inactivation by coenzyme A. Inactivated alpha-isopropylmalate and homocitrate synthases can be reactivated by dialysis, but not by adding excess substrate. Protection against coenzyme-A-mediated inactivation is provided by relatively high concentrations of the alpha-ketoacid substrate or the specific end product inhibitor of each of the two enzymes. The coenzyme-A-mediated inactivation of alpha-isopropylmalate synthase has been more closely investigated. It requires the presence of divalent metal ions, with Zn++being most effective. The inactivation does not require molecular oxygen. It occurs in the presence of low concentrations of substrates and is observed in toluene-treated cells. These results, together with evidence that alpha-isopropylmalate synthase and homocitrate synthase are located in the mitochondria, suggest a mechanism by which increasing intra-mitochondrial coenzyme A concentrations might serve as a signal of decreasing acetyl-coenzyme A levels, triggering a temporary inactivation of biosynthetic acetyl-coenzyme A-consuming reactions in order to channel the available acetyl-coenzyme A into the citrate cycle.
2-Isopropylmalate Synthase↗
Purification and properties of aminoendopeptidase from rat epidermis.
An aminoendopeptidase isolated from 2-day-old rat epidermis was purified to apparent homogeneity by the procedures of ammonium sulfate fractionation, DE-52 column chromatography, Sephadex G-200 gel filtration, and CM-52 and DEAE-Sepharose 6B column chromatography. Enzymatic activity was exhibited only in the presence of sulfhydryl compounds and further enhanced by addition of 5 mM EDTA. It was inhibited by p-chloromercuribenzoate, other sulfhydryl blocking reagents, and o-phenanthroline. The monomer form of the enzyme is Mr = 52,000 +/- 2,300 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, but a native form was considered to be Mr = 400,000 +/- 26,000 having an isoelectric point of pH 5.25. Among synthetic substrates the enzyme hydrolyzed amino acid 2-naphthylamide derivatives and L-leucine amine (L-LeuNH2) most effectively. N-alpha-benzoyl-DL-arginine-2-naphthylamide (BANA) was the only endopeptidase substrate for the enzyme and a competitive inhibitor for its aminopeptidase activity. Protein substrates have not yet been found. The pH optimum is 7.5 and in a range of pH 6.5-7.5 it is stable at 37 degrees C for 30 min but loses about 50% of its activity at 50 degrees C.
Animals↗