Effects of subunit V antibodies on the topology of the subunit and the activity of beef heart cytochrome-c oxidase.

Redox-sensitive epitopes on subunit V of beef heart cytochrome-c oxidase were demonstrated previously using polyclonal subunit-specific antibodies raised in rabbits. The antibodies only slightly inhibited electron transfer, and the accessibility of their epitopes depended on the presence of a membrane and on the redox state of the oxidase. The present paper describes additional preparations of antibodies raised against subunit V. These antibodies have an even higher subunit specificity, they are more than three times as inhibitory against electron transfer, and their binding does not require a membrane. Moreover, the redox-sensitive nature of their binding to detergent-dispersed oxidase is sensitive to the method of its isolation. We discuss inferences that can be drawn from a detailed quantitative comparison of the interactions of the two antibody preparations with the antigen in different environments. The techniques used in the comparison can be used to examine other perturbants of the oxidase as to their effects on specific segments of the enzyme.