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 M 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.