Temperature effects with immobilized yeast alcohol dehydrogenase in flow systems

Abstract

Activation energies were determined for the flow kinetics of yeast alcohol dehydrogenase (alcohol:NAD + oxidoreductase, EC 1.1.1.1) attached to nylon tubing, over a range of concentrations of the two substrates (NAD and ethanol) and at various flow rates. With NAD at saturating concentrations the activation energies showed little dependence on ethanol concentration and flow rate. Under these conditions the reaction shows hardly any diffusion control, and the activation energy for the chemical interaction at the surface is concluded to be about 9 kcal · mol −1. At saturating ethanol concentrations the activation energies increased significantly with increasing NAD concentration and flow rate. The limiting value at high NAD concentration and flow rate is consistent with the 9 kcal · mol −1 deduced for complete chemical control. Extrapolation to zero NAD concentrations and flow rates suggested a value of 4.2 kcal · mol −1 for the reaction under conditions of full diffusion control.