Interaction of reactive oxygen and nitrogen species with albumin- and methemoglobin-bound dinitrosyl-iron complexes

Destructive effect of superoxide anions O2- derived from KO2 or xanthine–xanthine oxidase system on dinitrosyl-iron complexes bound with bovine albumin or methemoglobin (DNIC-BSA or DNIC-MetHb) was demonstrated. The sensitivity of DNIC-BSA synthesized by the addition of DNIC with cysteine, thiosulfate or phosphate (DNIC-BSA-1, DNIC-BSA-2 or DNIC-BSA-3, respectively) to destructive action of O2- decreased in row: DNIC-BSA-1 > DNIC-BSA-3 > DNIC-BSA-2. The estimated rate constant for the reaction between O2- and DNIC-BSA-3 was equal to ∼107 M−1 s−1. However, hydrogen peroxide and tert-butyl hydrogenperoxide (t-BOOH) did not induce any noticeable degradation of DNIC-BSA-3 even when used at concentrations exceeding by one order of magnitude those of the complex. As to their action on DNIC-MetHb both hydrogen peroxide and t-BOOH-induced rapid degradation of the complex. Both agents could induce the process due to the effect of alkylperoxyl or protein-derived free radicals formed at the interaction of the agents with ferri-heme groups of MetHb. Peroxynitrite (ONOO−) could also initiate protein-bound DNIC degradation more efficiently in the reaction with DNIC-BSA-3. Higher resistance of DNIC-MetHb to peroxynitrite was most probably due to the protective action of heme groups on ONOO−. However, the analysis allows to suggest that the interaction of protein-bound DNICs with O2- is the only factor responsible for the degradation of the complexes in cells and tissues.