魚類におけるスクワレンおよびコレステロールの生合成-II.

Abstract

The biosynthesis of squalene and cholesterol from acetate-1-14C by the homogenate supernatant of carp hepatopancreas and from mevalonate-2-14C by that of rainbow trout liver was studied in vitro. The incubation was carried out with the addition of ATP, NAD, NADH, NADP and NADPH for four hours in the carp hepatopancreas preparation with acetate, and for two hours in the rainbow trout liver preparation with mevalonate under aerobic and anaerobic conditions at 30°C. The total radioactivities incorporated into the lipids of carp hepatopancreas preparations were less than 5% of the initial acetate, in which most of the label was found in the saponifiable fraction, whereas in the nonsaponifiable fraction the percentage radioactivities were not over 10%. Therefore, the net acetate incorporation into squalene and cholesterol does not exceed 0.5%. However, it was shown that the mevalonate incorporation by the rainbow trout liver preparation into such compounds was almost quantitative, if only one enantiomorph of DL-mevalonate were utilized on the pathway of cholesterogenesis. In general, the coenzyme requirements for cholesterol synthesis in the fish are not markedly different from those needed by land animals. As one of the cofactors required for the cyclization of squalene to lanosterol, molecular oxygen plays an important role as in the case of aerobic conditions. Moreover, the metabolic pathway from acetate or mevalonate via squalene to cholesterol and their relations as the precursor, intermediate and product are discussed.