MAGNETIC STATE OF THE ALPHA-3 CENTER OF CYTOCHROME-C-OXIDASE AND SOME OF ITS DERIVATIVES

The temperature dependence of the magnetic susceptibility was used to investigate the nature of the coupling between cytochrome a3 and Cu(B) in resting and oxidized cyanide- and formate-bound cytochrome oxidase. Resting and formate-bound enzymes were found to have strong antiferromagnetic coupling with an S = 5/2 cytochrome a3, results that were independent of the dispersing detergent and the enzyme isolation method. The cyanide-bound enzyme was heterogeneous, with a minor fraction showing intermediate strength antiferromagnetic coupling. The magnitude of this coupling was independent of the enzyme isolation method and depended moderately on the identity of the dispersing detergent. The major fraction of the cyanide-bound enzyme had a lowest energy state of M(s) = 0. The coupling constant for this fraction did not depend on the isolation technique or on the identity of the dispersing detergent. The use of glucose-glucose oxidase to deoxygenate samples influenced the susceptibility behavior of some preparations of both the resting and formate-bound enzymes, with results indicating an S = 3/2 cytochrome a3 in the resting enzyme samples. Retention of a 417-nm Soret band for formate-bound enzyme concomitant with peroxide-induced changes in susceptibility behavior indicates different sites of enzyme interactions for the formate ion and hydrogen peroxide.