Cardiolipin-protein interactions in the phosphate binding activity of a proteolipid from yeast mitochondria. Action of phospholipases A2 and C and of cations.

A proteolipid able to bind phosphate has been isolated from yeast mitochondria. During the purification the active protein was always associated with cardiolipin. The cardiolipin requirement for the phosphate binding activity of this proteolipid has been studied using controlled lipid depletion with two phospholipases A2 and with phospholipase C. Only phospholipase A2 from pig pancreas, that deacylated cardiolipin, promoted inhibition of the proteolipid activity (but never more than 70 per cent). Phospholipase A2 from snake venom did not inhibit the binding activity of the proteolipid. Using thin layer chromatography with two sequential solvents it was possible to separate two cardiolipin subspecies; one of them was preferentially hydrolysed by phospholipase C of Bacillus cereus, leading to inhibition of the proteolipid activity. Ca2+ complexed to cardiolipin stoichiometrically (1-1) inhibited the proteolipid activity. This effect could be due to a conformational change in the cardiolipin-protein association.