3-HYDROXY-3-METHYLGLUTARYL COENZYME A REDUCTASE FROM AVIAN LIVER - CATALYTIC PROPERTIES

The catalytic properties of microsomal 3-hydroxy-3-methylglutaryl coenzyme A reductase EC 1.1.1.34 from avian liver were investigated. Solubilized and highly purified reductase preparations were not cold labile. Enzymic activity remained unchanged following preincubation at 37.degree. C. The pH optimum was 6.8-7.0 and maximal catalytic activity was achieved with 2 mM dithiothreitol and 0.75 M KCl. The heat stability of the enzyme was studied and the addition of 0.75 M KCl, 0.8 mg/ml bovine serum albumin and 5 mM NADPH reduced the inactivation of the purified reductase associated with heat treatment at 65.degree. C. At 37.degree. C, 0.8 mg/ml bovine serum albumin enhanced the purified reductase activity by 100 (.+-. 20%). An improved assay was developed for the avian hydroxymethylglutaryl-CoA reductase and the specific activity of the purified enzyme increased from 1550 to 3300 nmol/min per mg. The Km values of solubilized and purified reductase for D-hydroxymethylglutaryl-CoA were 1.05 .mu.M and 1.62 .mu.M, and for NADPH, 1 mM and 263 .mu.M, respectively. The activities of the reductase preparations were non-competitively inhibited by coenzyme A, acyl-CoA esters and hydroxymethylglutarate. MgATP also reduced avian reductase activity. These modulators may play a role in the cellular regulation of the reductase activity.