PURIFICATION AND PROPERTIES OF CARNITINE ACETYLTRANSFERASE FROM CITRIC-ACID PRODUCING ASPERGILLUS-NIGER

Carnitine acetyltransferase was purified from the citric acid producin g A. niger mycelium with a protein band showing a relative molecular w eight of 77,000 and a pH optimum of 7.3. The Km values for the purifie d enzyme for acetyl-CoA and for carnitine were 0.1 mM and 1 mM, respec tively. Carnitine acetyltransferase was located both in the mitochondr ia and in the cytosol. Both mitochondrial and cytosolic enzyme were pu rified using ammonium sulfate precipitation, Mono Q and Superose 12 se paration. Regarding the localization, except for maximum velocity, the re were no differences observed in substrate specificity and inhibitio n. Inhibition of the enzyme with micromolar concentrations of Cu2+ cou ld contribute to a greater citric acid biosynthesis. Carnitine acetylt ransferase can be considered as an enzyme necessary for the transport of acetyl groups through mitochondrial membrane in both directions.