Purification and kinetic characteristics of pyruvate decarboxylase and ethanol dehydrogenase from Zymomonas mobilis in relation to ethanol production

Abstract

Alcohol dehydrogenase (EC 1.1.1.1) and pyruvate decarboxylase (EC 4.1.1.1) from Zymomonas mobilis were partially purified and characterized. Alcohol dehydrogenase exhibits a pH optimum at 6.5 and pyruvate decarboxylase a major peak at pH 6.0 and a minor one at pH 4.3. The molecular weights were estimated to be 147,300±14,700 and 219,700±20,400 daltons, respectively. Both enzymes exhibit hyperbolic saturation curves with their respective substrates. Whereas alcohol dehydrogenase was inhibited by ethanol (Ki=6.86×10−4 M) and NAD+ (Ki=1.44×10−4 M), no inhibition was observed with pyruvate decarboxylase at similar concentrations of ethanol. Neither of the enzymes responded to sulphydryl-binding reagents, but differed in their response to a number of divalent metals. The results are compared with those of the respective enzymes from yeast and discussed with a view towards ethanol production limitations by Zymomonas mobilis.