Production of acyl-carnitines from the metabolism of [U-14C]3-methyl-2-oxopentanoate by rat liver and skeletal muscle mitochondria.

A sensitive method of continuous on-line radio-high performance liquid chromatography (HPLC) was used to detect the specific radio-labelled acyl-carnitine esters derived from the oxidation of [U-14C]3-methyl-2-oxopentanoate by rat liver and muscle mitochondrial fractions. The recoveries of carnitine, acetyl-carnitine, propionyl-carnitine, 2-methylbutyryl-carnitine, and hexanoyl-carnitine were 98.7% (+/- 5.4; SEM, n = 3), 91.4% (+/- 7.6), 89.4% (+/- 5.2), 84.6% (+/- 6.8), and 87.9% (+/- 7.8), respectively, from quenched mitochondrial incubations. This method demonstrated that rat liver and muscle mitochondria generate acetyl-carnitine, propionyl-carnitine and 2-methylbutyryl-carnitine when incubated with [U-14C]3-methyl-2-oxopentanoate in the presence of carnitine. The production of acetyl-carnitine was almost similar in the 2 tissues. Muscle mitochondria produced higher amounts of propionyl-carnitine and 2-methylbutyryl-carnitine than liver mitochondria. These observations suggest a limited utilization of propionyl-CoA by muscle mitochondria which, through a mechanism of feed-back inhibition, may have contributed to the accumulation of 2-methylbutyryl-CoA. This study provides further evidence for the importance of carnitine in the modulation of the mitochondrial [acyl-CoA/[CoA] pool.