Studies on the delta 5-desaturation in ergosterol biosynthesis in yeast

Studies were carried out on the delta 5-desaturation reaction in ergosterol biosynthesis with a particulate fraction of cell-free extract of yeast. A reduced pyridine nucleotide coenzyme and molecular oxygen were required for the reaction. It was shown that the enzyme activity is located in a fraction corresponding to microsomes. The reaction was inhibited by KCN, but not by CO. Menadione and potassium ferricyanide inhibited the NADPH- and NADH-dependent reactions, respectively, and cytochrome c inhibited both of them. These results suggested an involvement in delta 5-desaturation of a mixed function oxidase system resembling that for the fatty acyl-CoA desaturation reaction.