ATP-Mg2+ reversal of the salt activation of membrane bound carnitine palmitoyltransferase activities of liver mitochondria.

The carnitine palmitoyltransferase (CPT) activities of the outer and the inner membranes of rat liver mitochondria were markedly activated by increase in the ionic strength of the assay medium. ATP at physiological concentrations in the presence of Mg2+ effectively reversed the above effect with octanoyl-CoA, but not with palmitoyl-CoA, as a substrate. Other nucleotides were unable to substitute for ATP. This ATP-Mg2+ effect on the CPT activity was not seen with mitochondria of heart or of skeletal muscles. The remarkable nucleotide, substrate and tissue specificity of these effects indicate that the above phenomenon may be functional in vivo to regulate the ability of liver mitochondria to utilize medium chain fatty acids via the carnitine-dependent route.