Amine:acetyl coenzyme A acetyltransferase from the soluble fraction of Hansenula ciferri: Isolation and properties

An enzyme (amine:acetyl coenzyme A acetyltransferase, EC 2.3.1.5) was partially purified from the 250 000 × g supernatant of extracts of the yeast Hansenula ciferri. It catalyzed the transfer of the acetyl group of acetyl-CoA to long-chain primary amines of 6-16 carbon atoms, as well as to water-soluble primary amines, such as glucosamine, histamine, tryptamine, serotonine, hydroxytyramine and noradrenaline, but not to polyamines, amino acids or sphingosine bases. The acetylation of the long-chain amines was inhibited by detergents, coenzyme A, butyryl or palmitoyl coenzyme A and by SH-inhibitors. Hyperbolic curves were obtained when reaction rates were measured as a function of increasing acetyl CoA concentrations, while maintaining a constant concentration of the amine. The curves were also hyperbolic when acetyl-CoA was maintained at a constant level and the concentrations of the water-soluble amines or normal amines of 6-10 carbon atoms were varied. With long-chain amines of 12-16 carbon atoms as the varying substrates, the v/S curves were hyperbolic to a certain concentration of the amine, above this concentration ("inversion point") reaction rates decreased. The inversion points of the three amines were close to their "critical micellar concentration". Serum albumin increased the reaction rates as well as the K_m values with the long-chain amines but not with the water-soluble compounds. These data suggest that the enzyme utilizes molecular solutions of the amines but is inhibited by their micellar aggregates.