Synthesis of Cholesterol in the Human Fetus: 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Activity of Liver Microsomes*

Abstract

The specific activity of 3-hydroxy-3-methylglu-taryl coenzyme A (HMG CoA) reductase in microsome-enriched fractions prepared from normal human fetal liver tissue was assessed. The mean specific activity was 0.58 ± 0.18 nmol mev-alonate formed min^–1 mg^–1 protein. The activity of the enzyme was inhibited by preincubation of microsomes with ATP (4 m.M) and was greatly reduced when microsomes were prepared from tissue homogenized in the presence of NaF (50 HIM). It can be computed that the activity of HMG CoA reductase in human fetal liver microsomes is adequate to provide cholesterol to meet the requirements of the fetal adrenal for steroid precursor provided that cholesterol synthesized in the fetal liver appears in the plasma in the form of low density lipoprotein.