THE EFFECT OF ANTIBODIES TO SUBUNIT-V OF CYTOCHROME-OXIDASE ON CYANIDE INHIBITION OF ELECTRON-TRANSFER

Binding of antibodies raised against subunit V of mammalian cytochrome oxidase to the intact membranous enzyme is redox-sensitive, suggestin g the existence of 'open' and 'closed' protein conformers (Freedman, J .A., Cooper, C.E., Leece, B., Nicholls, P. and Chan, S.H.P. (1988) Bio chem. Cell Biol. 66, 1210-1217). Similar open and closed states for th e oxygen-reacting site have been proposed to explain cyanide binding k inetics (Jensen, P., Wilson, M.T., Aasa, R. and Malmstrom, B.G. (1984) Biochem. J. 224, 829-837). We therefore examined cyanide inhibition o f oxidase activity polarographically and spectrophotometrically using soluble oxidase preincubated with and without anti-subunit V or non-im mune rabbit gamma-globulin. The subunit-specific antibody decreased th e cyanide 'on' rate and essentially eliminated the rapid phase of cyan ide binding. We conclude that (i), bound antibody blocks HCN binding; (ii), antibody and HCN probably bind to the same conformation of the o xidase and (iii), the 'open'-'closed' conformation change that modulat es binding of HCN may be similar to that which modulates antibody bind ing. The results are consistent with some reciprocating models of elec tron transfer and energy transduction by the oxidase (cf., Wikstrom, M .K.F., Krab, K. and Saraste, M. (1981) Cytochrome Oxidase: A Synthesis ).