The effect of free fatty acids (FFA) and lysophosphatidylcholine-oleoyl (lyso-PC) on proton gradients of pea stem microsomes and submitochondrial particles was studied. Linolenic (18:3), linoleic (18:2), oleic (18:1), palmitic (16:0) and stearic (18:0) acids collapsed the proton gradient generated by addition of ATP or PP to microsomes. When an artificial ΔpH was generated by NaOH, FFA did not induce any effect, but the subsequent addition of valinomycin dissipated the proton gradient. FFA were also able to discharge the ΔpH built up by the oligomycin-sensitive H+-ATPase of submitochondrial particles and the electrical potential generated by NADH oxidation in intact mitochondria. Free fatty acids stimulated NADH-dependent oxygen consumption by mitochondria and this effect was not abolished by ADP or carboxyatractyloside (CAtr). The effect of FFA increased with an increasing unsaturation of the acyl chain, while the length of the chain did not influence the activity. Lysophosphatidylcholine dissipated the proton gradient generated by H+-PPase of microsomes and H+-ATPase of submitochondrial particles, while the H+-ATPase of microsomes was slightly affected. In addition, lyso-PC stimulated NADH-dependent oxygen uptake by mitochondria. Also in this case, neither ADP nor CAtr inhibited this stimulated O2 consumption. These results show that FFA uncoupled oxidative phosphorylation of pea mitochondria and collapsed only proton electrochemical gradients in pea microsomes and submitochondrial particles. Therefore, in this regard FFA are similar to artificial protonophores, acting as proton carriers. The mechanism of action of lyso-PC appears to be more complex and different possible explanations are proposed.
