INHIBITORY EFFECT OF MG2+ ON THE PROTONOPHORIC ACTIVITY OF PALMITIC ACID

To discriminate whether fatty acids are uncouplers that cause accelera tion of State-4 respiration, associated with a decrease in the protonm otive force, or decouplers that increase respiration without associate d decrease in the protonmotive force, we examined the effect of palmit ate on functions of rat-liver mitochondria under various conditions. W e found that palmitate itself increases State-4 respiration, releases oligomycin-inhibited State-3 respiration, inhibits ATP synthesis and A TP reversible arrow P-i exchange reaction, and increases H+ permeabili ty in mitochondrial and model bilayer phospholipid membranes. Thus, pa lmitate is a classical uncoupler of oxidative phosphorylation. However , these effects were inhibited by Mg2+, due to rapid formation of a st able complex between palmitate and Mg2+.