PURIFICATION AND PROPERTIES OF CARNITINE ACETYLTRANSFERASE FROM HUMAN LIVER

Carnitine acetyltransferase was purified from the supernatant obtained after centrifugation of human liver homogenate to a final specific activity of 78.75 unit · mg−1 with acetyl‐CoA as a substrate. Human carnitine acetyltransferase is a monomer of 60.5 kDa with maximum activity in the presence of propionyl‐CoA and a pH optimum of 8.7. Apparent Km values for acetyl‐CoA are three times lower than for decanoyl‐CoA. Km values for L‐carnitine in the presence of acetyl‐CoA are six times lower than in the presence of decanoyl‐CoA. Km values for acetylcarnitine are three times lower than for octanoylcarnitine. The polyclonal antibodies against human carnitine acetyltransferase recognize a 60.5‐kDa peptide in the purified preparation of human liver and brain homogenates and in immunoblots of mitochondrial and peroxisomal fractions from human liver. Immunoprecipitation and SDS/PAGE analysis of 35S‐labelled proteins produced by human fibroblasts indicate that mitochondrial carnitine acetyltransferase is synthesized as a precursor of 65 kDa. We also purified carnitine acetyltransferase from the pellet obtained after centrifugation of liver homogenate. The pellet was extracted by sonication in the presence of 0.5% Tween 20. The chromatographic procedures for the purification and the kinetic, physical and immunological properties of pellet‐extracted carnitine acetyltransferase are similar to those of carnitine acetyltransferase purified from the supernatant of human liver homogenate. Copyright © 1990, Wiley Blackwell. All rights reserved