Inhibition by hydroxymalonate of malate dependent biosynthesis of progesterone in the mitochondrial fraction of human term placenta.

It has been shown that the conversion of cholesterol to progesterone by human term placental mitochondria incubated in the presence of malate or fumarate was inhibited by hydroxymalonate--an inhibitor of malic enzyme. No inhibition was observed when mitochondria were incubated in the presence of citrate or isocitrate. The degree of inhibition by hydroxymalonate of partly purified NAD(P)-linked malic enzyme activity was identical to that of both malate dependent pyruvate and progesterone formation by intact mitochondria. These data strongly support a previous suggestion that malic enzyme plays an important role in the malate dependent progesterone biosynthesis by human placental mitochondria.