title: Binding of malonyl-CoA to isolated mitochondria. Evidence for high- and low-affinity sites in liver and heart and relationship to inhibition of carnitine palmitoyltransferase activity.
abstract: [14C]Malonyl-CoA bound to intact mitochondria isolated from rat liver and heart in a manner consistent with the presence of two independent classes of binding sites in each tissue. The binding characteristics for mitochondria obtained from fed male rats were: for heart, KD(1) = 11-18nM, KD(2) = 30 microM, N1 = 7pmol/mg of protein, N2 = approx. 660pmol/mg of protein; for liver, KD(1) = 0.1 microM, KD(2) = 5.6 microM, N1 = 11pmol/mg of protein, N2 = 165pmol/mg of protein. In the presence of 40 microM-palmitoyl-CoA the characteristics of binding at the high-affinity sites were changed, so that for heart KD(1) = 0.26 microM, with no change in N1 and for liver KD(1) = approx. 2 microM, with N1 increased to approx. 40pmol/mg of protein. Differences between the two tissues in tightness of malonyl-CoA binding at the high-affinity sites explains the considerably greater sensitivity of heart CPT1 (overt form of carnitine palmitoyltransferase) to inhibition by malonyl-CoA [Saggerson & Carpenter, (1981) FEBS Lett. 129, 229-232; McGarry, Mills, Long & Foster (1983) Biochem. J. 214, 21-28]. Starvation (24h) did not change the characteristics of [14C]malonyl-CoA binding to liver mitochondria and did not alter the I50 (concentration giving 50% inhibition) for displacement of [14C]malonyl-CoA by palmitoyl-CoA. Therefore the decreased sensitivity of liver CPT1 to inhibition by malonyl-CoA in starvation [Saggerson & Carpenter (1981) FEBS Lett. 129, 225-228; Bremer (1981) Biochim. Biophys. Acta 665, 628-631] is not explained by differences in malonyl-CoA binding. Percentage occupancy of the high-affinity sites in heart mitochondria by malonyl-CoA correlated closely with percentage inhibition of CPT1 measured under similar conditions. This finding supports the proposal that the high-affinity binding sites are the functional sites mediating inhibition of CPT1 by malonyl-CoA. Similar experiments with liver mitochondria also suggested that the occupancy of high-affinity sites by malonyl-CoA regulates CPT1 activity. 5,5'-Dithiobis-(2-nitrobenzoic acid), which decreased the sensitivity of heart or liver CPT1 to inhibition by malonyl-CoA [Saggerson & Carpenter (1982) FEBS Lett. 137, 124-128], also decreased [14C]malonyl-CoA binding to the high-affinity sites of heart mitochondria. N1 values for [14C]malonyl-CoA binding to high-affinity sites in liver mitochondria were determined in various physiological states which encompassed a 7-fold range of CPT1 maximal activity (fed, starved, pregnant, hypothyroid, foetal). The N1 value did not change in these states.(ABSTRACT TRUNCATED AT 400 WORDS)
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism*; D000217:Acyltransferases / Q000037:antagonists & inhibitors*; D000818:Animals; D001665:Binding Sites; D002334:Carnitine O-Palmitoyltransferase / Q000037:antagonists & inhibitors*; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008316:Malonyl Coenzyme A / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism; D010171:Palmitoyl Coenzyme A / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D000214:Acyl Coenzyme A; D010171:Palmitoyl Coenzyme A; D008316:Malonyl Coenzyme A; D004228:Dithionitrobenzoic Acid; D000217:Acyltransferases; D002334:Carnitine O-Palmitoyltransferase