FATTY-ACIDS AS MODULATORS OF CYTOCHROME-C-OXIDASE IN PROTEOLIPOSOMES

The control of cytochrome c oxidase turnover in proteoliposomes by mem brane potential (Delta Psi) and by pH gradient (Delta pH) is probably kinetic in nature, and inhibition by valinomycin and stimulation by ni gericin indicate that Delta pH exerts a greater influence than does an equivalent Delta Psi. Oleic acid at 100 mu M removes all Delta Psi an d Delta pH control, whereas a similar concentration of palmitic acid i ncreases turnover but does not completely abolish control. Valinomycin acts synergistically with both fatty acids, indicating that the latte r can act as H+/K+ exchangers, but neither fatty acid alone markedly a ffects Delta pH, showing that they cannot fully mimic nigericin. Oleat e, but not palmitate, diminishes Delta Psi, and can move electrophoret ically as oleate anion. Submicromolar palmitic acid concentrations par tly stimulate turnover in Delta Psi- and Delta pH-controlled proteolip osomes, as reported by Labonia, Muller and Azzi [(1988) Biochem. J. 25 4, 130-145], which might represent a direct effect on cytochrome c oxi dase. The ubiquity of fatty acids in biological membranes suggests tha t these substances might be responsible for limiting respiratory contr ol and enzyme activity in vivo.