BIOLOGICAL REDUCTION OF AROMATIC NITROSO-COMPOUNDS - EVIDENCE FOR THEINVOLVEMENT OF SUPEROXIDE ANIONS

The in vitro formation of phenylhydronitroxide and 2-methylphenylhydro nitroxide free radicals from nitrosobenzene (NE) and 2-nitrosotoluene (NT), respectively, in either red blood cells (RBC) or RBC hemolysates , was confirmed by electron spin resonance spectroscopy (ESR). Free ra dicals were generated nonenzymatically from reaction of the respective nitroso compounds with a number of biological reducing agents as corr oborated by model studies of NB or NT with NAD(P)H. Under aerobic cond itions, phenylhydronitroxide and 2-methylphenylhydronitroxide underwen t a subsequent one-electron transfer to oxygen, which then resulted in the formation of superoxide anion (O-2(-)). The latter product was co nfirmed by the superoxide dismutase (SOD)-inhibitable reduction of cyt ochrome c (cyt c). Apparently, oxygen is needed for continuous formati on of the hydronitroxide radical derivatives. On the other hand, under anaerobic conditions, no phenylhydronitroxide radical was generated f rom NB in the presence of NADH, but the formation of phenylhydroxylami ne from NB was detected by the absorption spectrometry. These results suggest that oxygen is a preferential electron acceptor for hydronitro xide radical derivatives.