[21] Rat liver sterol Δ24-reductase

The biological reduction of desmosterol is readily demonstrated in the rat by injecting the labeled sterol intraportally and isolating radioactive cholesterol from the liver. The 24,25-double bond in a variety of sterols can be reduced by the same enzyme, and the more general name “sterol Δ -24-reductase” is more appropriate. Until the enzyme is solubilized and purified, it should be recognized that the name refers only to activities demonstrable in particulate preparations. As the substrates are added in suspension, little can be said with respect to kinetics or intimate mechanism of action of the enzyme. This chapter discusses its properties, substrate specificity, susceptibility to specific inhibitors, and role in sterol biogenesis. The chapter describes assay based on that employed by Steinberg, Avigan, and Goodman for reduction of desmosterol or lanosterol.