3-hydroxy-3-methylglutaryl-coa reductase from neonatal chick

Abstract 1. 1. The optimal conditions for identification of mevalonic acid as the product of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase are described, as well as the effect of different buffer constituents on the enzyme activity. 2. 2. Under the chosen assay conditions, reductase activity from neonatal chick liver increased with the incubation time up to 60 min and was proportional to the amounts of protein added in a range of 0.1–0.5 mg. 3. 3. The specific activity was maximal in brain and liver and lower in intestine of 6-day-old chicks. 4. 4. Thermostability of hepatic reductase was studied. When microsomal preparations were maintained at 4°C, reductase activity remained unchanged for 6 hr and decreased afterwards. 5. 5. Addition of 50 mM KF to the homogenization medium had no effect on the reductase activity. Similarly, preincubation of microsomal preparations with 105,000 g supernatants in the presence or absence of KF did not significantly increase the. reductase activity. These results suggest that HMG-CoA reductase was isolated from neonatal chick in the fully activated form.