The effect of lysophosphatidylcholine on the activity of various mitochondrial enzymes

The influence of lysophosphatidylcholine (LPC) on H(+)-ATPase, cytochrome oxidase (COX), glycerolphosphate dehydrogenase (GPDH) and malate dehydrogenase (MDH) was followed. The activities of H(+)-ATPase and COX increased with increasing LPC concentration up to 0.5 mg/mg protein when maxima were achieved. This activatory effect is LPC-specific, because Lubrol-treated or frozen-thawed mitochondria showed lower activities of these enzymes. H(+)-ATPase was not influenced by higher concentration of LPC, while COX activity decreased with increasing amount of LPC. The activity of GPDH decreased at very low concentration of LPC and was not further modified at higher LPC concentration. In an attempt to find the concentration of LPC necessary for a complete permeabilization of inner mitochondrial membrane we followed the influence of lysolipid on the release of MDH activity from the mitochondrial matrix. The full activity of this enzyme was obtained with a concentration 0.75 mg LPC/mg protein indicating that mitochondria were completely broken. Our data indicate that LPC significantly affects activity of enzymes connected with mitochondrial membrane and can be useful for evaluation of the importance of phospholipid microenvironment for the enzyme function.