Poly (ADP-ribose) synthetase activity in rat testis mitochondria

A quite active poly (ADP-ribose) synthetase was found in isolated rat testis mitochondria. Similar levels of activity were found in mitochondria isolated from bull and hamster testis. In contrast, mitochondria isolated from rat brain or liver, and demembraned sperm, showed negligible activity. Centrifugation of testis mitochondria through a linear sucrose gradient, showed that, poly (ADP-ribose) synthetase cosediment together with succinatecytochrome c reductase and mitochondrial proteins. Furthermore, treatment with digitonin indicated that, the enzyme is localized in the inner membrane-matrix complex. Finally, kinetic studies demonstrated that, the apparent Km for NAD⁺ of the mitochondrial enzyme, was 22 μM compared with 210 μM for the nuclear enzyme.