Effects of monoclonal antibodies to bovine and Paracoccus denitrificans cytochromes c on reactions with oxidase, reductase and peroxidase.

The effects of monoclonal antibodies to bovine and Paracoccus denitrificans cytochromes c (Kuo, L.M. and Davies, H.C. (1983) Mol. Immunol. 20, 827-838) in the reactions of the cytochromes c with cytochrome c oxidase, reductase and peroxidase were studied. Spectrophotometric assays were employed, under conditions where binding of cytochrome c to the enzymes appears to be rate-limiting. Less than stoichiometric amounts of antibodies to P. denitrificans cytochrome c added to the cytochrome rendered some of it nonoxidizable or nonreducible by the P. denitrificans membrane-bound electron transport system and decreased the rate constant with the remaining cytochrome c. The antibodies appear to affect both electron transport reactions (blocking effects) with the oxidase and reductase and binding effects (effects on rate constants) and to distinguish between the two. Different ratios of antibody site to cytochrome c gave different extents of blocking of the reductase as compared with the oxidase reaction. Differences were also apparent in the effect of these antibodies on the reaction of yeast peroxidase and the oxidase with the P. denitrificans cytochrome c. Antibodies to bovine and P. denitrificans cytochromes c had considerably less effect on the reactions of the bovine cytochrome with bovine oxidase and reductase. One antibody was inhibitory to the oxidase reaction with bovine cytochrome c, but not to that with the reductase. Also, an antibody which inhibited the oxidase reaction had no effect on the reaction with yeast peroxidase. The data give evidence that the interaction areas on cytochrome c for oxidase and reductase and peroxidase are not identical, although they may be nearby.