title: Carnitine acyltransferase activities in rat brain mitochondria. Bimodal distribution, kinetic constants, regulation by malonyl-CoA and developmental pattern.
abstract: Carnitine palmitoyltransferase and carnitine octanoyltransferase activities in brain mitochondrial fractions were approx. 3-4-fold lower than activities in liver. Estimated Km values of CPT1 and CPT2 (the overt and latent forms respectively of carnitine palmitoyltransferase) for L-carnitine were 80 microM and 326 microM, respectively, and K0.5 values for palmitoyl-CoA were 18.5 microM and 12 microM respectively. CPT1 activity was strongly inhibited by malonyl-CoA, with I50 values (concn. giving 50% of maximum inhibition) of approx. 1.5 microM. 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 KD(1), KD(2), N1 and N2 were 18 nM, 27 microM, 1.3 pmol/mg of protein and 168 pmol/mg of protein respectively. Neither CPT1 activity, nor its sensitivity towards malonyl-CoA, was affected by 72 h starvation. 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 beta-oxidation in brain. CPT1 activity relative to mitochondrial protein increased slightly from birth to weaning (20 days) and thereafter decreased by approx. 50%.
mesh_terms: D000217:Acyltransferases / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D002333:Carnitine Acyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002334:Carnitine O-Palmitoyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008316:Malonyl Coenzyme A / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D013569:Synapses / Q000201:enzymology
chemical_list: D008316:Malonyl Coenzyme A; D000217:Acyltransferases; D002333:Carnitine Acyltransferases; C030162:carnitine octanoyltransferase; D002334:Carnitine O-Palmitoyltransferase