OPTIMIZATION OF BAKERS-YEAST ALCOHOL-DEHYDROGENASE ACTIVITY IN AN ORGANIC-SOLVENT

Alcohol dehydrogenase from baker's yeast (YADH) has been used to oxidize an unsaturated alcohol, 3-methyl-2-buten-1-ol (UOL), to the corresponding unsaturated aldehyde, 3-methyl-2-butenal (UAL), in heptane. The influence of total system water content, coenzyme NAD to enzyme molar ratio prior to catalyst preparation, and enzyme concentration on the conversion and redox reaction rates were investigated. The optimal water content was found to be 0.25-0.5% (v/v), and a molar ratio of NAD to enzyme of 2.15 is recommended on the basis of economic and kinetic data. A maximal initial reaction rate for YADH of 0.02 mM/min/mg was observed under optimal conditions. The minimum cofactor turnover number was also determined under all conditions, and the effect of doping the catalyst with extra binding sites for NAD was investigated. The effect of substrate on enzyme stability has also been investigated. Interestingly, when the enzyme is preincubated in heptane, its initial activity can be increased 3-fold.