The role of a carrier protein in cholesterol and steroid hormone synthesis by adrenal enzymes

Abstract

Squalene and sterol carrier protein (SCP) of liver, known to be required for cholesterol synthesis by liver microsomal enzymes, functions with adrenal microsomal enzymes (Δ 7 -sterol Δ 5 -dehydrogenase and Δ 5,7 -sterol Δ 7 -reductase) catalyzing cholesterol synthesis from sterol precursors. Adrenal preparations contain a heat-stable protein which functions similarly to liver-SCP with adrenal and liver enzymes. Liver-SCP also can participate with an adrenal enzyme (solubilized from an acetone powder of mitochondria) in the conversion of cholesterol to pregnenolone. These findings indicate that an SCP-like protein not only participates in cholesterol synthesis and transport in the adrenal, but also in the initial steps of cholesterol metabolism to steroid hormones.