Palmitic and stearic acids bind Ca2+ with high affinity and form nonspecific channels in black-lipid membranes. Possible relation to Ca2+-activated mitochondrial pores

A mitochondrial hydrophobic component that forms Ca2+-induced nonspecific i on channels in black-lipid membranes (Mironova et al., 1997) has been purif ied and its nature elucidated. It consists of long-chain saturated fatty ac ids-mainly palmitic and stearic. These fatty acids, similar to the mitochon drial hydrophobic component. bind Ca2+ with high affinity in comparison wit h unsaturated fatty acids, saturated fatty acids with shorter aliphatic cha ins, phospholipids, and other lipids, Ca2+-binding is inhibited by Mg2+ but not by K+. For palmitic acid, the K-d for Ca2+ was 5 muM at pH 8.5 and 15 muM at pH 7.5, with the B-max of 0.48 +/- 0.08 mmol/g. This corresponds to one Ca2+ ion for eight palmitic acid molecules. The data of IR spectroscopy confirm that Ca2+ does not form ionic bonds with palmitic and stearic acid s under hydrophobic conditions. It has been found that in the presence of C a2+ palmitic and stearic acids, but not unsaturated FFA induce a nonspecifi c permeability in black-lipid membranes. Addition of Ca2+ in order to induc e the permeability transition, increases the extractable amount of palmitic and stearic acids, the effect being prevented by a phospholipase A(2) inhi bitor. The possible involvement of palmitic and stearic acids in the mitoch ondrial nonspecific permeability is discussed.