Abstract
The formation of copper complexes with bis[cyclo( histidylhistidine )] copper(II) was determined potentiometrically; the maximum coordination number was four deprotonated histidine residues per Cu(II) ion. This complex mimicks the active center of Cu/Zn superoxide dismutase (superoxide:superoxide oxidoreductase, EC 1.15.1.1). Its absorption spectrum showed a broad band above 600 nm as compared with the 670- to 680-nm band of the enzyme. Its CD spectrum had a negative 600- to 605-nm band and a more intense positive band near 780 nm. The band positions were identical with, and the intensities were higher than, those of the enzyme, but the corresponding bands had opposite signs. This can be attributed to the difference in the distorted planar structure between the complex and enzyme. The complex catalyzed the dismutation of superoxide anion; the activity was 1/10th that of the enzyme on a molar basis, but about three times that of the enzyme on a weight basis.