J. Biol. Chem., Vol. 255, Issue 18, 8394-8397, 09, 1980
Mechanism of the stimulation of branched chain oxoacid oxidation in liver by carnitine
ME May, RP Aftring and MG Buse
The oxidation of 4-methyl-2-oxopentanoate (alpha-ketoisocaproate) by rat
liver mitochondria was shown to be independent of exogenous coenzyme A and
exogenous NAD+. Carnitine stimulated the oxidation of 4-
methyl-2-oxopentanoate in rat liver homogenates and mitochondria;
octanoate, DL-octanoylcarnitine, 4-pentenoate, and 3-methylbutyrate
(isovalerate) were inhibitory, and 2-bromopalmitate had no effect. Addition
of carnitine was found to increase the export from the mitochondria of
acylcarnitines derived from 4-methyl-2-oxopentanoate in the presence of
absence of 4-pentenoate but not in the presence of octanoylcarnitine. It is
concluded that the branched chain oxoacid dehydrogenase is localized on the
inner surface of the inner mitochondrial membrane and that it is regulated
in part by the intramitochondrial levels of branched chain fatty acyl-CoA
esters and/or free CoA.