Human and rat tumour cells possess mitochondrial carnitine palmitoyltransferase I and II: effects of insulin.

In order to investigate the long-chain fatty acid oxidative capacity of tumour cells, carnitine palmitoyltransferase I (CPT I) and CPT II were selected for study because they are rate-limiting regulatory enzymes. Measurable activities of both CPT I and CPT II were detected in several human and rat tumour cell types and in mouse fibroblasts. The activities were comparable with those previously reported for rat liver CPT I and II, ranging from 1-3 nmoles/min/mg protein for both CPT I and II. Walker 256 tumour tissue also contained detectable CPT I and II activities, thereby demonstrating that tumour tissue in vivo also has the capacity for the processing of fatty acyl CoA's in the mitochondrion. The possible regulation of tumour CPT I and II was investigated using the hormone insulin, both in vitro and in vivo. Insulin was found to increase CPT II activity in the T24/83 human bladder tumour in vitro and in the Walker 256 rat tumour in vivo. The results suggest that insulin may exert some control over the activity of CPT II in certain types of tumour. In contrast, insulin was without effect on CPT I activity in any of the tumours studied, either in vitro or in vivo.