Fatty acid uncoupling of oxidative phosphorylation in rat liver mitochondria

Abstract

Free fatty acids (FFA) are known to uncouple oxidative phosphorylation in mitochondria. However, their mechanism of action has not been elucidated as yet. In this study we have investigated in detail the patterns of uncoupling by the FFA oleate and palmitate in rat liver mitochondria and submitochondrial particles. The patterns of uncoupling by FFA were compared to uncoupling induced by the ionophores valinomycin (in the presence of K+) and gramicidin (in the presence of Na+) and the proton translocator carbonyl cyanide m-chlorophenylhydrazone (CCCP). The most striking difference in the pattern of uncoupling relates to the effect on the proton electrochemical potential gradient, delta mu H. Uncoupling by ionophores, particularly valinomycin, is associated with and most likely caused by a major reduction of delta mu H. In contrast, uncoupling by FFA is not associated with a significant reduction of delta mu H, indicating another mechanism of uncoupling. We suggest the use of the term decouplers for uncoupling agents such as FFA and general anesthetics that do not collapse the delta mu H [Rottenberg, H. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 3313-3317]. The protonophore CCCP and to some extent the ionophore gramicidin indicate a mixed mode of uncoupling since their effect on delta mu H is moderate when compared to that of valinomycin. Another distinguishing feature of uncouplers that collapse the delta mu H is their ability to stimulate ADP-stimulated respiration (state 3) further. Decouplers such as FFA and general anesthetics do not stimulate state 3 respiration.(ABSTRACT TRUNCATED AT 250 WORDS)