Purification and catalytic properties of alcohol acethl-transferase from hansenula anomala

Abstract

The volatile compounds produced by H.anomala IFO 0127 were identified by gas chromatographic analysis. Many kinds of higher alcohols and esters, especially, ethyl acetate, i-butyl acetate, i-amyl acetate and phenethyl acetate had a main role on the fruit-like flavors of this culture broth. Among these, i-butyl acetate was formed mainly from i-butyl alcohol and acetylCoA with the crude enzyme prepared by ammonium sulfate fractionation, while a small quantity was formed from i-butyl alcohol and acetic acid. To elucidate the mechanism of ester formation from the corresponding alcohol, the acetic-ester synthesizing enzyme was purified about 50-fold by ammonium sulfate fractionation, gel filtration on Sephadex G-150 and ion exchange chromatography on DEAE-Sephadex A-50. It was found that the purified enzyme catalyzed the ester formation reaction from the corresponding alcohol using only acetyl-CoA. The enzyme was the most active at $30\,^\circ\!C$ and PH 7. It was least active against $C_3$-alcohol among $C_2-C_5$ alcohols, and slightly more active against straight-chain alcohols than against branched-chain alcohols with the same carbon number. The enzyme was strongly inhibited by heavy metal ions and unsaturated fatty acids, especially by increasing the degree of unsaturation of fatty acid with the same carbon number. The enzyme was also inhibited by high concentration of substrate itself, alcohol, and the $K_m$ and $K_i$ values for the formation of acetic-esters from the corresponding alcohols were 1.51 and 0.77 for i-butyl alcohol, 0.72 and 0.45 for i-amyl alcohol, respectively.