Electron paramagnetic resonance studies of cobalt-copper bovine superoxide dismutase.

1. EPR spectra of cobalt-copper bovine superoxide dismutase at liquid nitrogen and liquid helium temperature show that the two metal centers are magnetically coupled. The temperature dependence of the spectra indicates that this coupling arises from an exchange interaction. 2. The EPR spectrum of the Co(I1) of the enzyme can only be seen after reduction of the Cu(II), at very low temperature. It is typical of tetrahedral coordination which is distorted in a particular way. The EPR parameters are gr N_ 4, gii N 2, D = 11.5 cm-r. No feature indicating interaction between the two Co(I1) centers is observed. 3. Anions such as CNand NOdo not affect the EPR spectrum of Co(I1) significantly, but only modify the spectrum of Cu(I1). It is concluded that the Co(I1) site (and presumably the native Zn(l1) site) can be described as distorted tetrahedral, strongly spin-coupled to the Cu(I1) and therefore very near to it, and noninteracting with the other Co(I1) site and with solvent molecules.