title: Functional size of rat hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase as determined by radiation inactivation.
abstract: The functional molecular weight of rat liver 3-hydroxy-3-methylglutaryl-CoA reductase was determined by radiation inactivation. Both isolated hepatic microsomes and primary hepatocytes were irradiated with high energy electrons at -135 degrees C, and the residual microsomal enzyme activity was subsequently determined. The loss of enzyme activity in both irradiated microsomes and microsomes isolated from irradiated hepatocytes followed a single exponential decay which corresponded to a molecular mass of 200 kDa. This minimal molecular size of the functional enzyme was unaffected by either addition of cholestyramine to the rat diet or addition of 25-hydroxycholesterol plus mevalonate to the isolated rat hepatocytes. In addition, surviving enzyme protein was determined by immunoprecipitation of radiolabeled enzyme from hepatocytes that had been incubated with [35S]methionine before irradiation. The target size for loss of the monomer subunits was 98 kDa. The simplest interpretation of these results is that rat liver 3-hydroxy-3-methylglutaryl-CoA reductase in situ is a noncovalently linked dimer of the Mr = 97,200 enzyme subunit.
mesh_terms: D000818:Animals; D004307:Dose-Response Relationship, Radiation; D006903:Hydroxymethylglutaryl CoA Reductases / Q000096:biosynthesis / Q000528:radiation effects*; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008715:Methionine / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology; D008970:Molecular Weight; D051381:Rats
chemical_list: D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D008715:Methionine; D006903:Hydroxymethylglutaryl CoA Reductases