Interference with the determination of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and its properties by a microsomal enzymic activity

Abstract

Rat liver microsomes and microsomal extracts contain an enzymic activity which competes with 3-hydroxy-3-methylglutaryl coenzyme A reductase for 3-hydroxy-3-methylglutaryl coenzyme A. The presence of this activity in enzyme preparations causes errors in the determination of reductase activity and its properties. This contaminant can be removed by gel filtration using Bio-Gel A 1.5m, by washing the microsomes, or by incubating the microsomal extract at 37 °C. The K m 's of the reductase (free of this competing enzymic activity) for d-3-hydroxy-3-methylglutaryl coenzyme A and NADPH are 1.3 and 26 μ m, respectively.