ACETYL-COENZYME-A DEACYLASE ACTIVITY IN LIVER IS NOT AN ARTIFACT - SUBCELLULAR-DISTRIBUTION AND SUBSTRATE-SPECIFICITY OF ACETYL-COENZYME A DEACYLASE ACTIVITIES IN RAT-LIVER

Whole liver and isolated liver mitochondria release free acetate, esespecially under conditions of increased fatty acid oxidation. Rat liver contains acetyl-CoA deacylase (EC 3.1.2.1) activity (0.72 .mu.mol/min per g wet wt of liver at 30.degree. C and 0.5 mM-acetyl-CoA). At 0.5 mM-acetyl-CoA 73% of total enzyme activity was found in the mitochondria, 8% in the lysosomal fraction and 19% in the postmicrosomal supernatant. Mitochondrial subfractionation shows that mitochondrial acetyl-CoA deacylase activity is restricted to the matrix space. Mitochondrial acetyl-CoA deacylase showed almost no activity with either butyryl- or hexanoyl-CoA. Acetyl-CoA hydrolase activity from purified rat liver lysosomes exhibited a very low affinity for acetyl-CoA (apparent Km > 15 mM compared with an apparent Km value of 0.5 mM for the mitochondrial enzyme) and reacted at about the same rate with acetyl-, n-butyryl- and hexanoyl-CoA. The findings of Costa and Snoswell according to which mitochondrial acetyl-CoA deacylase was considered to be an artifact resulting from the combined actions of acetyl-CoA-L-carnitine acetyltransferase (EC 2.3.1.7) and acetylcarnitine hydrolase were not confirmed. The results are in line with the concept that free acetate released by the liver under physiological conditions stems from the intramitochondrial deacylation of acetyl-CoA.