Characterization of poly(ADP-ribose)polymerase from Crithidia fasciculata: enzyme inhibition by beta-lapachone.

Crithidia fasciculata poly(ADP-ribose)polymerase (PARP) has been isolated and partially purified. This is the first PARP isolated from trypanosomatids; it requires DNA and histone for activity, using NAD(+) as substrate. Thiol compounds specially dithiothreitol essentially contributed to PARP stability during purification and to PARP activity during assays. Nicotinamide, 3-aminobenzamide, theophylline, histamine, histidine, N-ethylmaleimide, p-chloromercuribenzoic acid, p-chloromercuriphenylsulfonic acid and o-iodosobenzoate inhibited PARP, thus confirming enzyme identity. PARP was also inhibited by the Fe(II)/H(2)O(2) Fenton system. beta-Lapachone inhibited PARP, apparently by direct interaction with the enzyme.

Effects of mansonones on lipid peroxidation, P450 monooxygenase activity, and superoxide anion generation by rat liver microsomes.

Several structurally related ortho-naphthoquinones isolated from Mansonia altissima Chev (mansonones C, E and F) (a) inhibited NADPH-dependent, iron-catalyzed microsomal lipid peroxidation; (b) prevented NADPH-dependent cytochrome P450 destruction; (c) inhibited NADPH-supported aniline 4-hydroxylase activity; (d) inhibited Fe(III)ADP reduction by NADPH-supplemented microsomes; (e) stimulated superoxide anion generation by NADPH-supplemented microsomes; and (f) stimulated ascorbate oxidation. ESR investigation of ascorbate-reduced mansonone F demonstrated semiquinone formation. Mansonone C had a greater effect than mansonones E and F on NADPH-dependent lipid peroxidation, O2- production and ascorbate oxidation, whereas mansonone E was more effective than mansonones C and F on aniline 4-hydroxylase activity. Mansonones E and F did not inhibit hydroperoxide-dependent lipid peroxidation, cytochrome P450 destruction or microsomal aniline 4-hydroxylase activity. Mansonone C inhibited to a limited degree tert-butyl hydroperoxide-dependent lipid peroxidation, this inhibition being increased by NADPH. Mansonone A, a tetrahydro orthonapthoquinone derivative, was in all respects relatively less effective than mansonones C, E and F. It is postulated that mansonones C, E and F inhibited microsomal lipid peroxidation and cytochrome P450 catalyzed reactions by diverting reducing equivalents from NADPH to dioxygen, but mansonone C (including its reduced form) may also exert direct antioxidant activity.