Subcellular distribution and characteristics of ciprofibroyl-CoA synthetase in rat liver: Its possible identity with long-chain acyl-CoA synthetase

Abstract

The subcellular distribution and characteristics of ciprofibroyl-CoA synthetase were studied in rat liver and compared with those of long-chain acyl-CoA synthetase (palmitate as substrate) which, as already known, is distributed among mitochondria, microsomes and peroxisomes. Upon differential centrifugation, the subcellular distribution of ciprofibroyl-CoA synthetase followed closely that of palmitoyl-CoA synthetase and was specifically inactivated in the mitochondrial fraction by freezing and thawing, a behaviour already described for palmitoyl-CoA synthetase. Both enzyme activities were found to co-purify through several steps from rat liver microsomes. By using a partially purified enzyme, the activation of ciprofibrate to its acyl-CoA ester followed Michaelis-Menten kinetics with an apparent K(m) of 0.63±0.1mM. Ciprofibroyl-CoA synthetase was competitively inhibited by 25 and 50μM-palmitic acid. Higher concentrations of the fatty acid resulted in a mixed type of inhibition. Conversely, ciprofibrate up to 0.5mM was found to inhibit competitively palmitoyl-CoA synthetase, whereas higher concentrations also resulted in a mixed inhibition. The highest activity of ciprofibroyl-CoA synthetase was found in fat and liver homogenates. The distribution of the enzyme in different rat tissues was similar to that of palmitoyl-CoA synthetase. The present results suggest that long-chain acyl-CoA synthetase and ciprofibroyl-CoA synthetase activities reside in identical or closely related proteins.