[4] 3-Hydroxy-3-methylglutaryl-CoA reductases from pea seedlings

This chapter describes 3-hydroxy-3-methylglutaryl-CoA reductases from pea seedlings. The enzyme HMG-CoA reductase (3-hydroxy-3-methylglutaryl-CoA reductase; EC 1.1.1.34) catalyzes the conversion of HMG-CoA to meva- Ionic acid, the first intermediate used solely for isoprenoid synthesis. Thus, the enzyme catalyzes the reductive deacylation of HMG-CoA; the thiol-esterified carboxyl group (C-I of HMG-CoA), is reduced to a primary alcoholic group, on C-5 of mevalonic acid. The stoichiometry shown derives from studies on the enzyme from microorganisms and mammals, and comparison of spectrophotometric and radiochemical assay data for the enzyme from plants indicates similar stoichiometry. While the procedures described below have been established using pea seedling tissues, the major features probably apply equally well to other tissues. However, minor modifications may be necessary in some cases, and the sections on Compartmentation, Isolation Variables, and enzyme stability, may help to identify isolation problems.