Stereochemistry of the formation of lactaldehyde and acetoin produced by the pyruvate decarboxylases of yeast (Saccharomyces sp.) and Zymomonas mobilis: different Boltzmann distributions between bound forms of the electrophile, acetaldehyde, in the two enzymatic reactions

Pyruvate decarboxylase from Saccharomyces sp. catalysed the formation of acetoin of predominantly the opposite configuration than that obtained using the enzyme from Zymomonas mobilis. A similar result was obtained for the lactaldehyde formed in the pyruvate decarboxylase-catalysed decarboxylation of glyoxylate in the presence of acetaldehyde. The results are interpreted in terms of different Boltzmann distributions for the two enzymes between the enzyme–substrate complexes of acetaldehyde bound on its re and si faces respectively.