THE ANALOGOUS REACTION OF DISCHIFF BASE COORDINATED COPPER AND CU2ZN2SUPEROXIDE-DISMUTASE WITH NITRIC-OXIDE

In addition to the well known catalytically accelerated O-2(.-) dismut ation, Cu2Zn2 superoxide dismutase (SOD) reversibly reduces NO to NO- with the consequence of a prolonged half-life of NO. This alternative reactivity was examined in the presence of the intact CuZn enzyme and a diSchiff base copper complex prepared from putrescine and pyridine-2 -aldehyde (Cu-PuPy) which is known as a convenient active center analo g of the former copper protein, The reaction of this SOD mimick with N O and NO- was monitored by electronic absorption and electron paramagn etic resonance (EPR) spectroscopy via the formation of nitrosylmyoglob in. Cu-PuPy reacted up to three times faster with NO compared with Cu2 Zn2 SOD and 15 times faster in comparison with CuSO4 and copper EDTA. The oxidation rate of NO- by Cu-PuPy was up to 300% higher compared wi th the reactivities of CuSO4 and Cu EDTA. Cu2Zn2SOD reacted with NO- t o a neglible extent only. Catalytic characteristics could be observed in the course of the oxidation of NO- in concentrations between 1 and 20 mu M copper. Disturbances of the EPR properties suggested a modific ation of the chemical environment at the copper sites in both the copp er complex and the enzyme, As a consequence, no further reactions of t he nitrogen monoxides with the respective active centers were seen, In conclusion, Cu-PuPy appears to be an efficient moderator of the bioch emical reactivity of nitrogen monoxides attributable to the observed i ncreased half-life of NO.