Purification of carnitine carrier from rat brain mitochondria

Brain mitochondria isolated from rats of different age were solubilized with Triton X-100 and the detergent extract was subjected to chromatography on dry hydroxyapatite and celite. The highest specific activity (110 mumol/10 min per g protein) measured after reconstitution of isolated proteins into phosphatidylcholine vesicles correlated with the appearance of a polypeptide with a molecular mass of 33,000. Activity of the carnitine carrier, both in isolated mitochondria and in the reconstituted system, varied with animal age, being twice higher in suckling rats than in adults. After reconstitution, the carnitine exchange showed sensitivity to SH groups modifying reagents, N-ethylmaleimide and mersalyl. Acetyl, propionyl and palmitoyl esters of carnitine decreased carnitine/carnitine exchange. Short and medium chain acyl derivatives were more potent inhibitors, pointing to a different substrate specificity of carnitine carrier in brain, in comparison with other tissues.