Malonyl-CoA inhibition of peroxisomal carnitine octanoyltransferase.
Although the malonyl-CoA sensitivity of peroxisomal carnitine octanoyltransferase (COT) is reportedly lost on solubilization, we show that malonyl-CoA does inhibit the purified enzyme. Assay conditions such as buffer composition, pH, acyl-CoA substrate and the presence or absence of BSA can affect the observed inhibition. When assayed in the absence of BSA, COT shows simple competitive inhibition by malonyl-CoA. The Ki value for inhibition of purified COT is high (106 microM) compared with physiological concentrations (1-6 microM) and other short-chain acyl-CoA esters inhibit COT to the same degree. However, when COT is assayed in intact peroxisomes, the Ki for malonyl-CoA is almost 20-fold lower than found with the purified enzyme, whereas inhibition by other short-chain acyl-CoA esters does not change significantly. Several features of the inhibition of peroxisomal COT, including the specificity of malonyl-CoA over other short-chain acyl-CoA esters, resemble those of carnitine palmitoyltransferase (CPT)-I, suggesting that the regulation of COT and CPT-I in parallel may be necessary for the control of cellular fatty acid metabolism.
A'Bháird
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Department of Biochemistry and Biophysics, University of California, San Francisco 94143.
Ramsay
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RR
D000818:Animals; D002333:Carnitine Acyltransferases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008316:Malonyl Coenzyme A / Q000494:pharmacology*; D008830:Microbodies / Q000201:enzymology*; D013379:Substrate Specificity
D008316:Malonyl Coenzyme A; D002333:Carnitine Acyltransferases; C030162:carnitine octanoyltransferase