Effects of dl-2-bromopalmitoyl-CoA and bromoacetyl-CoA in rat liver and heart mitochondria. Inhibition of carnitine palmitoyltransferase and displacement of [14C]malonyl-CoA from mitochondrial binding sites

Abstract

The overt form of carnitine palmitoyltransferase (CPT1) in rat liver and heart mitochondria was inhibited by DL-2-bromopalmitoyl-CoA and bromoacetyl-CoA. S-Methanesulphonyl-CoA inhibited liver CPT1. The inhibitory potency of DL-2-bromopalmitoyl-CoA was 17 times greater with liver than with heart CPT1. Inhibition of CPT1 by DL-2-bromopalmitoyl-CoA was unaffected by 5,5′-dithiobis-(2-nitrobenzoic acid) or (in liver) by starvation. In experiments in which DL-2-bromopalmitoyl-CoA displaced [14C]malonyl-CoA bound to liver mitochondria, the KD (competing) was 25 times the IC50 for inhibition of CPT1 providing evidence that the malonyl-CoA-binding site is unlikely to be the same as the acyl-CoA substrate site. Bromoacetyl-CoA inhibition of CPT1 was more potent in heart than in liver mitochondria and was diminished by 5,5′-dithiobis-(2-nitrobenzoic acid) or (in liver) by starvation. Bromoacetyl-CoA displaced bound [14C]malonyl-CoA from heart and liver mitochondria. In heart mitochondria this displacement was competitive with malonyl-CoA and was considerably facilitated by L-carnitine. In liver mitochondria this synergism between carnitine and bromoacetyl-CoA was not observed. It is suggested that bromoacetyl-CoA interacts with the malonyl-CoA-binding site of CPT1. L-Carnitine also facilitated the displacement by DL-2-bromopalmitoyl-CoA of [14C]malonyl-CoA from heart, but not from liver, mitochondria. DL-2-Bromopalmitoyl-CoA and bromoacetyl-CoA also inhibited overt carnitine octanoyl-transferase in liver and heart mitochondria. These findings are discussed in relation to inter-tissue differences in (a) the response of CPT1 activity to various inhibitors and (b) the relationship between high-affinity malonyl-CoA-binding sites and those sites for binding of L-carnitine and acyl-CoA substrates.