Inhibition by Mn2+ of citrate supported progesterone biosynthesis in mitochondrial fractions of human term placentae

Mitochondrial fraction prepared from human term placentae were incubated with [14C]-cholesterol in the presence of citrate, cis-aconitate or isocitrate. A stimulatory effect of these metabolites on cholesterol to progesterone conversion was found. In contrast to the other metabolites tested, citrate supported progesterone biosynthesis was found to be inhibited by manganese ions. This effect occurred in intact mitochondria only and was accompanied by a decreased citrate consumption.