Superoxide dismutase activity of Cu(Tyr)2 and Cu, Co-erythrocuprein.
Crystalline Cu(Tyr)2 and homogeneous Cu2Co2-erythrocuprein were prepared. The reactivity of each chelated Cu2 compound with superoxide was studied by pulse radiolysis at pH 7.6 +/- 0.1 and compared with the reactivity of native erythrocuprein (superoxide dismutase). Superoxide anions were generated by a 40-ns pulse of 1.81-MeV electrons. The yield of O2 ranged between 6 - 60 muM. The kinetics of the spontaneous O2 decay were second order; in the presence of Cu2 complexes the reaction was first order with respect to O2. Taking into account the effect of the different Cu2 concentrations on the O2 decay, second-order rate constants for the reaction of chelated Cu2 with O2 were obtained. For an equivalent of Cu2 in either erythrocuprein or Cu, Co-erythrocuprein, a numerical value of 1.3 +/- 0.1 x 10(9) M-1S-1 was calculated. Surprisingly, the same value was obtained employing Cu(Tyr)2. The highest rate constant was measured for the hydrated Cu2 (2.7 x 10(9) M-1S-1). In the presence of a biologically significant chelating agent such as serum albumin, a marked decrease in the Cu2aq-induced superoxide dismutation was observed. This was not the case when the dismutation in the presence of either the Cu2 of native erythrocuprein or Cu, Co-erythrocuprein, or those Cu2 ions chelated with tyrosine or certain di- and tripeptides was measured.