Abstract
As HOU et al. (1, 2) mentioned, cell-free extract from methanol-grown yeasts catalyzes the oxidation reaction of secondary alcohols to methyl ketones. Recently, we found that glucose-grown yeasts also produce secondary alcohol dehydrogenase that is constitutively formed. Among several methanol-grown yeasts, Hansenula polymorpha P-5 was the most suitable enzyme source because of its thermal stability and broad substrate specificity. In addition to the secondary alcohols, primary alcohols and 1, 2-propanediol are also oxidized by the cell-free extract of H. polymorpha P-5. The oxidation of secondary alcohols to methyl ketones by immobilized yeast cells was examined and compared with the oxidation by the cell suspensions. Oxygen was essential for the conversion of 2-propanol to acetone. The secondary alcohol dehydrogenase activity of the immobilized cells was not affected by pH shock from 7.0 to 3.5, but with the cell suspension it was affected. The optimun pH for the cell suspension was about 8.5, but the immobilized yeast cells had a broad optimum pH range from 5.0 to 8.5. Only an 8% decrease in the enzyme activity of the immobilized yeast cells occurred when the pH was below 4.0. For the immobilized yeast cells, the tolerance concentration of the secondary alcohol dehydrogenase to acetone was up to 5% (v/v). However, with cell suspensions, the enzyme was not tolerant to acetone. The optimal enzyme activity of cell suspensions lasted 2 days; that of immobilized yeast cells lasted 3 days. The enzyme activity of immobilized cells could be restored with glucose medium.
