Decay studies of dmpo-spin adducts of free radicals produced by reactions of metmyoglobin and methemoglobin with hydrogen peroxide

초록

The 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) spin adduct of myoglobin (Mb) or hemoglobin (Hb) was formed when metmyoglobin (MetMb) or methemoglobin (MetHb) reacted with H<inf>2</inf>O<inf>2</inf> in the presence of DMPO, and both decayed with half-life of a few minutes. The DMPO spin adduct of Mb decayed with biphasic kinetics with k<inf>1</inf> = 0.645 min-1 and k<inf>2</inf> = 0.012 min-1, indicating that the spin adduct consisted of two kinetically heterogeneous species, stable and unstable ones. The DPMO spin adduct of Hb, however, was homogeneous. Decay of both spin adducts was accelerated in the presence of tyrosine, tryptophan or cysteine, but not phenylalanine, methionine or histidine. The decay obeyed the first order kinetics at varying concentrations of the spin adducts. The decay was accelerated by denaturation and proteolysis of protein moiety. The decay rate was not affected by the extra addition of MetMb or MetHb to each spin adduct. The decay rate of the spin adduct of Mb was increased by hematin in the presence of H<inf>2</inf>O<inf>2</inf> and decreased by catalase. Decay of stable spin adduct of Mb, however, was not significantly changed under any experimental conditions used. These results led us to conclude that instability of the DMPO-spin adducts of Mb and Hb is due to intramolecular redox reactions between the spin adducts and amino acid residues and/or products of the reaction between heme and H<inf>2</inf>O<inf>2</inf>. © 1995 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.

키워드