The effects of mevinolin on the thiol/disulfide exchange between 3-hydroxy-3-methyglutaryl-coenzyme A reductase and glutathione.
The feeding of mevinolin plus cholestyramine to rats results in the production of a form of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR-CM) having thiol/disulfide redox properties different from those of 3-hydroxy-3-methylglutaryl-CoA reductase isolated from animals which had been given only cholestyramine (HMGR-C). The second-order rate constant for the inactivation of HMGR-CM by GSSG is 7-fold slower than for HMGR-C, while the second-order rate constant for the reactivation of oxidized enzyme by GSH is 100-fold slower. However, in the presence of saturating concentrations of both substrates, the rate constants for thiol/disulfide exchange are similar for both forms of the enzyme. HMGR-CM behaves as if a protein-glutathione mixed disulfide having a Kox of 27 +/- 4 is formed at equilibrium. In contrast, HMGR-C has previously been shown to form a protein-protein disulfide (Cappel, R. E., and Gilbert, H. F. (1988) J. Biol. Chem. 263, 12204-12212). Both forms of the enzyme are more difficult to oxidize thermodynamically in the presence of saturating levels of both substrates. For HMGR-CM, NADPH alone has no effect on the equilibrium constant for oxidation, but hydroxymethylglutaryl-CoA alone makes the enzyme approximately twice as difficult to oxidize. Under physiological conditions, HMGR-CM is thermodynamically more difficult to oxidize than HMGR-C. HMGR-C can be converted to HMGR-CM by in vitro treatment with mevinolinate. A direct or indirect interaction of mevinolin with HMGR-C results in some persistent, as yet undefined, structural alteration which inhibits the formation of a protein-SS-protein disulfide upon oxidation by glutathione disulfide.
Cappel
R E
RE
Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030.
Gilbert
H F
HF
D000818:Animals; D002792:Cholestyramine Resin / Q000008:administration & dosage; D004220:Disulfides / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism*; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology / Q000378:metabolism; D008148:Lovastatin / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D013816:Thermodynamics
D004220:Disulfides; D013438:Sulfhydryl Compounds; D002792:Cholestyramine Resin; D008148:Lovastatin; D006903:Hydroxymethylglutaryl CoA Reductases; D005978:Glutathione