Glutathione, enzyme activation

The importance of having adequate supplies of NADPH for the regeneration of these various enzymes cannot be over emphasized. In normal situations this cofactor can be adequately provided by the reductive pentose phosphate pathway. Monitoring the activity of the pentose phosphate pathway has been proposed as a unique way to study the metabolic response to oxidative stress, since the glutathione peroxidase activity is coupled via glutathione reductase to the enzyme glucose-6-phosphate dehydrogenase (Ben Yoseph et ah, 1994). 

In an analogous reaction catalyzed by 2,5-dihydroxypyridine 5,6-dioxygenases from various strains (Scheme 3d), the hydrolysis products maleamate and formate were identified. The latter enzymes require Fe2+ and a thiol donor such as dithiothreitol, cysteine, or glutathion for activity. 

C. carpio 10 during exposure for 96 h, significant alterations were recorded in lipid peroxidation rate, hemoglobin concentration, and erythrocyte antioxidant enzymes, that is, catalase, superoxide dismutase, and glutathione peroxidase activities 20... 

Fung and colleagues examined the metabolic conversion of organic nitrates in sub-cellular fractions of bovine coronary artery smooth muscle cells [66, 67]. They found NO-generating capacity to be present in membrane fractions and, with the use of marker enzymes, identified plasma membrane as the primary location. The enzyme involved in bioconversion was not glutathione-S-transferase [68] and differed from those that catalyse activation of organic nitrites [69]. Partial purification [70] established that the molecular sizes of the native enzyme and subunits were approximately 200 kDa and 58 kDa respectively, and that enzymic activity depends on the presence of a free thiol group. 

K8. Kerppola, W., Nikkila, E. A., and Pitkanen, E., Serum TPN linked enzymes glucose-6-phosphate dehydrogenase, isocitric dehydrogenase and glutathione reductase activities in health and various disease states. Acta Med. Scand. 164, 357-305 (1959). 

This EAD-dependent enzyme [EC 1.6.4.2] catalyzes the reaction of NADPH with glutathione disulfide to produce NADP+ and two glutathione molecules. The enzyme activity is dependent on a redox-active disulfide group in each of the active sites. 

Rats, exposed for 7 days to 85% Oj, survived for more than 4 days in 100% Oj, when control rats died within 3 days. They showed a 50% increase of SOD in their lungs. With guinea-pigs, hamsters, and mice there was no increase of pulmonary SOD and no tolerance was developed This increase in pulmonary SOD at 80% O or more was only observed with 10-day old and not with 25-day old rats. Catalase and glutathione peroxidase were increased with both groups There are, however, modifications at the cellular level besides the increase of the enzyme activities. 

The enzyme activity is significantly inhibited by Tiron and 8-hydroxyquinoline, but not by a,a -dipyridyl and o-phenanthroline. The addition of thiol compounds such as cysteine, 2-mercaptoethanol and glutathione, and thiol inhibitors such as p-chloromercuribenzoate, N-ethylmaleimide and HgCl2 also markedly decreases the enzyme activity. The Michaelis constants of the enzyme are as follows 2-nitropropane (2.13 x 10-2M), nitroethane (2.43 x 10-2M), 3-nitro-2-pentanol (6.8 x 10 3M), 1-nitropropane (2.56 x 10-2 M) and oxygen (3.63 x 10 4M with 2-nitropropane)199. ... 

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