NADPM BINDING AND CONTROL OF CATALASE COMPOUND-II FORMATION - COMPARISON OF BOVINE, YEAST, AND ESCHERICHIA-COLI ENZYMES

1. NADPH binds to bovine catalase and to yeast catalases A and T, but not to Escherichia coli catalase HPII. The association was demonstrate d using chromatography and fluorimetry. Bound NADPH fluoresces in a si milar way to NADPH in solution. 2. Bound NADPH protects bovine and yea st catalases against forming inactive peroxide compound II either via endogenous reductant action or by ferrocyanide reduction during cataly tic activity in the presence of slowly generated peroxide. 3. Bound NA DPH reduces neither compound I nor compound II of catalase. It apparen tly reacts with an intermediate formed during the decay of compound I to compound II; this postulated intermediate is an immediate precursor of stable compound II either when the latter is formed by endogenous reductants or when ferrocyanide is used. It represents therefore a new type of hydrogen donor that is not included in the original classific ation of Keilin and Nicholls [Keilin, D. and Nicholls, P. (1958) Bioch im. Biophys. Acta 29, 302-307] 4. A model for NADPH action is presente d in which concerted reduction of the ferryl iron and of a neighbourin g protein free radical is responsible for the observed NADPH effects. The roles of migrant radical species in mammalian and yeast catalases are compared with similar events in metmyoglobin and cytochrome c pero xidase reactions with peroxides.