ABSTRACT: Squalene synthetase (EC 126.96.36.199) and squalene epoxidase (EC 1.14 99.7) activities have been measured in cell-free extracts
of wild type yeast grown in aerobic and semianaerobic conditions as well as in sterol-auxotrophic mutant strains grown aerobically.
The results show that both enzymes are induced resulting in an almost two- to five-fold increase in enzymatic activities in
mutant strains containing limited sterol amounts and are repressed in the wild type strain cultured in anaerobiosis in excess
of sterol. The results show also that squalene epoxidase is repressed by lanosterol, and that the mevalonic acid pool may
regulate squalene synthetase levels.
The large change in the activities of the two enzymes, depending on the sterol needs of the cells, as well as their low specific
activities in comparison with those of the enzymes involved in the early stages of sterol synthesis strongly suggests that
squalene synthetase and squalene epoxidase are of importance in regulating the amount of sterol synthesized by yeast.
Lipids 04/1989; 24(12):1020-1023. · 2.13 Impact Factor