Specificity of carnitine action on fatty acid oxidation by heart muscle

Abstract

Carnitine (ß-hydroxy, γ-trimethylammonium butyrate), at concentrations of 10–5 m and more, increased the oxidation of long-chain fatty acids severalfold by heart muscle particulates incubated under optimal conditions. CoA dependency could be demonstrated in the presence of carnitine but not in its absence. Of a variety of compounds tested for carnitinelike activity, only acetylcarnitine and ß-hydroxy, γ-dimethylaminobutyrate ("norcarnitine") influenced palmitate oxidation in the assay system. Activity was abolished by removal of the hydroxyl group on the ß carbon; by replacement of the carboxyl group with either a cyano, an alcohol, or an amide grouping; or by substitution of an amino group for the trimethylammonium moiety of the molecule. Nonspecifically tritium-labeled carnitine was not degraded by heart particulates during incubation, indicating that carnitine acted catalytically to enhance fatty acid oxidation. The physiological significance of the data was discussed.