Carnitine acyltransferase activities in rat brain mitochondria. Bimodal distribution, kinetic constants, regulation by malonyl-CoA and developmental pattern

Abstract

1. Carnitine palmitoyltransferase and carnitine octanoyltransferase activities in brain mitochondrial fractions were approx. 3-4-fold lower than activities in liver. 2. Estimated K(m) values of CPT1 and CPT2 (the overt and latent forms respectively of carnitine palmitoyltransferase) for L-carnitine were 80 μM and 326 μM, respectively, and K0.5 values for palmitoyl-CoA were 18.5 μM and 12 μM respectively. 3. CPT1 activity was strongly inhibited by malonyl-CoA, with I50 values (concn. giving 50% of maximum inhibition) of approx. 1.5 μM. In the absence of other ligands, [2-14C]malonyl-CoA bound to intact brain mitochondria in a manner consistent with the presence of two independent classes of binding sites. Estimated values for K(D(1)), K(D(2)), N1 and N2 were 18 nM, 27 2mM, 1.3 pmol/mg of protein and 168 pmol/mg of protein respectively. 4. Neither CPT1 activity, nor its sensitivity towards malonyl-CoA, was affected by 72 h starvation. 5. Rates of oxidation of palmitoyl-CoA (in the presence of L-carnitine) or of palmitoylcarnitine by non-synaptic mitochondria were extremely low, indicating that neither CPT1 nor CPT2 was likely to be rate-limiting for β-oxidation in brain. 6. CPT1 activity relative to mitochondrial protein increased slightly from birth to weaning (20 days) and thereafter decreased by approx. 50%.