Modulation of catalase peroxidatic and catalatic activity by nitric oxide

Previously, we found that catalase enhanced the protection afforded by supe roxide dismutase to Escherichia coli against the simultaneous generation of superoxide and nitric oxide (Brunelli et al., Arch. Biochem. Biophys. 316: 327-334, 1995, Hydrogen peroxide itself was not toxic in this system in the presence or absence of superoxide dismutase. We therefore investigated whe ther catalase might consume nitric oxide in addition to hydrogen peroxide. Catalase rapidly formed a reversible complex stoichiometrically with nitric oxide with the Soret band shifting from 406 to 426 nm and two new peaks ap peared at 540 and at 575 nm, consistent with the formation of a ferrous-nit rosyl complex. Catalase consumed more nitric oxide upon the addition of hyd rogen peroxide. Conversely, micromolar concentrations of nitric oxide slowe d the catalase-mediated decomposition of hydrogen peroxide. Catalase pretre ated with nitric oxide and hydrogen peroxide regained full activity after d ialysis. Our results suggest that catalase can slowly consume nitric oxide while nitric oxide modestly inhibits catalase-dependent scavenging of hydro gen peroxide. The protective effects of catalase in combination with supero xide dismutase may result from two actions; reducing peroxynitrite formatio n by scavenging nitric oxide and by scavenging hydrogen peroxide before it reacts with superoxide dismutase to form additional superoxide. (C) 2001 El sevier Science Inc.