Effects of carnitine and acetylcarnitine isomers on mitochondrial respiration

Mitochondrial respiration was studied in the presence of carnitine or acetyl-carnitine isomers. The results demonstrate that 15 mM L-acetylcarnitine stimulates oxygen consumption by approximately 25%. D-acetylcarnitine (15 mM) had a slight inhibitory effect whereas racemic DL-acetylcarnitine (15 mM) markedly inhibited mitochondrial respiration. Similarly racemic DL-carnitine showed approximately 60% inhibition of mitochondrial respiration. L-carnitine or D-carnitine showed no significant effect on oxygen consumption. Further studies will be required to establish whether the carnitine or acetylcarnitine isomers competitively inhibit the acylcarnitine translocase systems of the mitochondrial membrane.