title: Inhibition of superoxide dismutase by nitroprusside and electron spin resonance observations on the formation of a superoxide-mediated nitroprusside nitroxyl free radical.
abstract: Nitroprusside appears to inhibit the known types of superoxide dismutases irrespective of their metal prosthetic group and regardless of the source from which the enzymes were isolated. Thus the copper-zinc enzyme from bovine erythrocyte or Neurospora crassa behaved identically as did the manganese enzymes from Escherichia coli or red alga and the iron enzyme from E. coli and a blue-green alga. The inhibition was dose dependent with a Ki = 2.5 X 10(-5) for nitroprusside. Nitroprusside does not bind to the copper moiety of copper-zinc enzyme and seems to compete with O2- for superoxide dismutase. These inhibitions by nitroprusside, which were elicited not only in purified enzymes but also in crude soluble extracts of biological samples, were rapidly reversible. Nitroprusside was found to react with O2- to form a paramagnetic species with three absorption lines of equal width with a separation AN = 15.0 G and a g value of 2.028. The spin adduct appears to be a nitroxide radical and was stable for several minutes.
mesh_terms: D000458:Cyanobacteria / Q000201:enzymology; D004578:Electron Spin Resonance Spectroscopy; D004912:Erythrocytes / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology; D005292:Ferricyanides / Q000494:pharmacology*; D005609:Free Radicals; D007700:Kinetics; D009492:Neurospora crassa / Q000201:enzymology; D009599:Nitroprusside / Q000494:pharmacology*; D013482:Superoxide Dismutase / Q000037:antagonists & inhibitors*
chemical_list: D005292:Ferricyanides; D005609:Free Radicals; D009599:Nitroprusside; D013482:Superoxide Dismutase