Testicular sterols: I. Incorporation of mevalonate and acetate into sterols by testicular tissue from rats

Abstract

Conditions have been established for the incorporation of labeled acetate and mevalonate into sterols of rat testicular tissue. Maximal rates of incorporation into the nonsaponifiable lipids were obtained with phosphate buffer (0.05 M, pH 7.4), sodium chloride (0.05 M), glucose (0.033 M), potassium (0.024 M), magnesium (0.006 M), suspended testicular tissue (approximately 50–75 mg. of protein), and acetate (0.0028 M) or d, l-mevalonate (0.00050 M). Unlabeled mevalonate (2.7 × 10 −8−2.7 × 10 −5 M) depressed the incorporation of labeled acetate (3.2 × 10 −5 M). Labeled lanosterol, squalene, cholesterol, and acyclic alcohols (farnesol and nerolidol) were purified with unlabeled carriers. In addition, small amounts of activity were associated with minor fractions of sterols (possibly 24,25-dihydrolanosterol and Δ 7-cholestenol). After incubation with acetate-1-C 14 in vitro, relative amounts of activity in the various fractions of the nonsaponifiable lipids were: squalene, 34%; lanosterol and companion C 30−, C 29−, and C 28−sterols, 19%; cholesterol and companion C 27−sterols, 16%; and unfractionated steroids, 26%. After incubation with mevalonate-2-C 14, the relative activities were 32, 21, 12, and 8%, respectively, of the total label that was isolated in the nonsaponifiable fraction. Labeled acetate was incorporated into all fractions of testicular sterols in vivo. Labeled acetate and mevalonate were not incorporated into sterols by cell-free homogenates of testicular tissue in fortified media; similar homogenates metabolized labeled lanosterol.