Glutathion reductase inhibition

Morean N, Martens T, Flenry MB, Leroy JP. Metabolism of oltipraz and glutathione reductase inhibition, Biochem Pharmacol 1990 40 1299-1305,... 

Garlic s proven mechanisms of action include (a) inhibition of platelet function, (b) increased levels of two antioxidant enzymes, catalase and glutathione peroxidase, and (c) inhibition of thiol enzymes such as coenzyme A and HMG coenzyme A reductase. Garlic s anti-hyperlipidemic effects are believed to be in part due to the HMG coenzyme A reductase inhibition since prescription medications for hyperlipidemia have that mechanism of action (statins). It is unknown whether garlic would have the same drug interactions, side effects, and need for precautions as the statins. 

Glutathione reductase (GR) catalyzes the reduction of oxidized glutathione (GSSG) to reduced glutathione (GSH) using NADPH provided from the hexose monophosphate pathway. GR, a ubiquitous flavoenzyme, maintains a high value of two for the GSH/GSSG ratio in the red blood cells. l,3-Bis(2-chloroethyl)-nitrosourea (BCNU) selectively inhibits cellular GR. GR is composed of two identical subunits, each of molecular mass 50 kDa (S8). The three-dimensional structure and mechanism of catalysis have been established for human GR (K17). 

Determination of the Inhibition Constant for Inhibition of Glutathione Reductase by Glucose-6-Phosphate... 

The inhibition constant for the process in which the enzyme glutathione reductase is inhibited by G6P was determined by measuring the initial rate of the oxidation of NADPH at various concentrations of GSSG. This procedure was repeated four times, each time with a separate concentration of the inhibitor G6P All the solutions were prepeared in 0.1 M Tris buffer pH 8 containing 10 mM MgCl2 and 0.94 mM EDTA. 

Cohen, M.D., A.C. Sen, and C.-I. Wei. 1987. Ammonium metavanadate complexation with glutathione disulfide A contribution to the inhibition of glutathione reductase. Inorg. Chim. Acta 138 91-93. 

Witte AB, Anestal K, Jerremalm E, Ehrsson H, Amer ES (2005) Inhibition of thioredoxin reductase but not of glutathione reductase by the major classes of alkylating and platinum-containing anticancer compounds. Free Radic Biol Med 39 696-703... 

The stability of EH2 is very species dependent. All of the above results refer to the pig heart enzyme and, where tested, to other mammalian species. It was initially reported that no long wavelength absorption was observed upon reduction of E. coli enzyme with NADH 109), but reduction by 1 equivalent of NADH or dihydrolipoamide leads to the formation of 25% of the maximal 2-electron-reduced species 108) and similar results are obtained with the Azotobacter enzyme 114)- That this species is the catalytically important one in the E. coli enzyme as well as in the mammalian enzyme has also been demonstrated 50). Reduction with dihydrolipoamide in the rapid reaction spectrophotometer at 2° results in the full formation of EH2 followed by the slow k = 13 min, 1 mAf dihydrolipoamide) four-electron reduction. The spectrum of EHa generated in this way is shown in Fig. 7 and is identical with that of the pig heart enzyme. The 2-electron-reduced form, EHj of lipoamide dehydrogenase of spinach 99) may be somewhat unstable however, spectrally it is difficult to distinguish between instability and formation of the EHa-NADH complex (see above) on the basis of available spectral data. Either phenomenon could lead to inhibition by excess NADH. In glutathione reductase it is possible that the complex can be rapidly reoxidized by glutathione 53). 

The early kinetic studies on glutathione reductase did not include investigation of product inhibition, so vital to a proper interpretation of kinetic data in the elucidation of the mechanism 247, 248). In the one case where product inhibition patterns were observed, they were not interpreted by more recent kinetic theory 40). Subsequent kinetic analyses see below), in which product inhibition patterns have been obtained, were either completed prior to the discovery of the EH2-NADPH complex... 

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