Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.2.1.22 (cystathionine beta-synthase)
 965 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hydrogen sulfide (H2S) is a recently identified gasotransmitter that may mediate hypoxic responses in vascular smooth muscle. H2S also appears to be a signaling molecule in mammalian non-vascular smooth muscle, but its existence and function in non-mammalian non-vascular smooth muscle have not been examined. In the present study we examined H2S production and its physiological effects in urinary bladder from steelhead and rainbow trout (Oncorhynchus mykiss) and evaluated the relationship between H2S and hypoxia. H2S was produced by trout bladders, and its production was sensitive to inhibitors of cystathionine beta-synthase and cystathionine gamma-lyase. H2S produced a dose-dependent relaxation in unstimulated and carbachol pre-contracted bladders and inhibited spontaneous contractions. Bladders pre-contracted with 80 mmol l(-1) KCl were less sensitive to H2S than bladders contracted with either 80 mmol l(-1) KC2H3O2 (KAc) or carbachol, suggesting that some of the H2S effects are mediated through an ion channel. However, H2S relaxation of bladders was not affected by the potassium channel inhibitors, apamin, charybdotoxin, 4-aminopyridine, and glybenclamide, or by chloride channel/exchange inhibitors 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid disodium salt, tamoxifen and glybenclamide, or by the presence or absence of extracellular HCO3-. Inhibitors of neuronal mechanisms, tetrodotoxin, strychnine and N-vanillylnonanamide were likewise ineffective. Hypoxia (aeration with N2) also relaxed bladders, was competitive with H2S for relaxation, and it was equally sensitive to KCl, and unaffected by neuronal blockade or the presence of extracellular HCO3-. Inhibitors of H2S synthesis also inhibited hypoxic relaxation. These experiments suggest that H2S is a phylogenetically ancient gasotransmitter in non-mammalian non-vascular smooth muscle and that it serves as an oxygen sensor/transducer, mediating the effects of hypoxia.
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PMID:Hydrogen sulfide mediates hypoxia-induced relaxation of trout urinary bladder smooth muscle. 1688 71

Cystathionine beta-synthase (CBS) is a homocysteine metabolizing enzyme that contains pyridoxal phosphate (PLP) and a six-coordinate heme cofactor of unknown function. CBS was inactivated by peroxynitrite, the product of nitric oxide and superoxide radicals. The IC(50) was approximately 150microM for 5microM ferric CBS. Stopped-flow kinetics and competition experiments showed a direct reaction with a second-order rate constant of (2.4-5.0)x10(4)M(-1)s(-1) (pH 7.4, 37 degrees C). The radicals derived from peroxynitrite, nitrogen dioxide and carbonate radical, also inactivated CBS. Exposure to peroxynitrite did not modify bound PLP but led to nitration of Trp208, Trp43 and Tyr223 and alterations in the heme environment including loss of thiolate coordination, conversion to high-spin and bleaching, with no detectable formation of oxo-ferryl compounds nor promotion of one-electron processes. This study demonstrates the susceptibility of CBS to reactive oxygen/nitrogen species, with potential relevance to hyperhomocysteinemia, a risk factor for cardiovascular diseases.
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PMID:Inactivation of cystathionine beta-synthase with peroxynitrite. 1973 48