The analogous reaction of diSchiff base coordinated copper and Cu2Zn2 superoxide dismutase with nitric oxide

In addition to the well known catalytically accelerated O2 dismutation, 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 analog of the former copper protein. The reaction of this SOD mimick with NO and NO− was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopy via the formation of nitrosylmyoglobin. Cu-PuPy reacted up to three times faster with NO compared with Cu2Zn2 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 with the reactivities of CuSO4 and Cu EDTA. Cu2Zn2SOD reacted with NO− to a neglible extent only. Catalytic characteristics could be observed in the course of the oxidation of NO− in concentrations between 1 and 20 μM copper. Disturbances of the EPR properties suggested a modification of the chemical environment at the copper sites in both the copper complex and the enzyme. As a consequence, no further reactions of the nitrogen monoxides with the respective active centers were seen. In conclusion, Cu-PuPy appears to be an efficient moderator of the biochemical reactivity of nitrogen monoxides attributable to the observed increased half-life of NO.