Carnitine palmitoyltransferase and carnitine octanoyltransferase activities in liver, kidney cortex, adipocyte, lactating mammary gland, skeletal muscle and heart

Transfer of long chain fatty acids through the inner membrane of mitochondria appears to require two pools of carnitine palmitoyl transferase (CPT), one latent, the other overt [l-5]. The relative proportions of these latent and overt forms of CTP has mainly been studied in liver mitochondria. A medium chain carnitine acyltransferase (COT, carnitine octanoyltransferase) has also been reported in heart and liver [6,7]. This activity appears to be distinct from CPT and from carnitine acetyltransferase (CAT), but its physiological role is uncertain. Until recently [8], it had not been established whether COT in heart or liver mitochondria showed latency. There has been considerable interest in the observation that overt CPT activity in liver mitochondria is potently inhibited by malonyl CoA [9]. CPT activity in heart mitochondria [8] and COT in liver [lo] and heart [8] mitochondria are also extremely sensitive to malonyl CoA. It was therefore of interest to investigate the sensitivity of these activities to malonyl CoA in a wide range of tissues to see if regulation by this effector has general applicability. The relative activities of the latent and overt forms of CPT and COT have also been measured and are found to vary widely from tissue to tissue.