Studies on the Biosynthesis of 5α-Cholestan-3β-ol

Abstract

1. Cholest-4-en-3-one 5α-reductase of rat liver, which catalyzes the conversion of cholest-4-en-3-one to 5α-cholestan-3-one, was shown to be localized mainly in the microsomal fraction. 2. Cholest-4-en-3-one 5α-reductase required reduced nicotinamide adenine dinucleotide phosphate as electron donor and differed from the known Δ4-3-ketosteroid 5α-reductases by being inactive in the presence of reduced nicotinamide adenine dinucleotide. 3. The microsomal cholest-4-en-3-one 5α-reductase preparations did not reduce the double bond of cholest-4-en-3β-ol, cholesterol, or cholest-5-en-3-one. 4. The action of cholest-4-en-3-one 5α-reductase was inhibited by certain Δ4-3-ketosteroids and by cholest-5-en-3-one, and appeared to be stimulated by cholesta-4,6-dien-3-one and by cholesta-5,7-dien-7-one. 5. It was concluded that the microsomal cholest-4-en-3-one 5α-reductase of rat liver is not identical with the known microsomal Δ4-3-ketosteroid 5α-reductases.