Long Chain Base-Acetyl Coenzyme A Acetyltransferase from the Microsomes of Hansenula ciferri

Microsomes of the yeast, Hansenula ciferri NRRL Y-1031, F-60-10, contain an enzyme (long chain base-acetyl coenzyme A acetyltransferase, EC 2.3 . 1) which catalyzes the transfer of the acetyl moiety of acetyl coenzyme A to both the amino and hydroxyl groups of the sphingosine bases; a separation of these two transfer reactions could not be achieved. The enzyme also catalyzed an acetyl transfer to the hydroxyl groups of N-acetylated sphingosine bases and to the amino groups of normal aliphatic primary amines of 6 to 18 carbon atoms, but not to compounds such as p-nitroaniline, glucosamine, secondary amines, or primary alcohols. A similar enzyme was not found in rat organs nor in extracts of pigeon liver acetone powder. The reaction rates were directly proportional to enzyme concentration and time of incubation. The optimal pH depended on the type of buffer used. The reaction rates could be correlated to the charge conferred upon the micelles of the bases by the various buffers. The reaction was not reversible and an exchange between the products and substrates could not be shown. It was inhibited by coenzyme A but not by the lipid products.