Enzymes involved in the glycidaldehyde (2,3-epoxy-propanal) oxidation stepin the kinetic resolution of racemic glycidol (2,3-epoxy-1-propanol) by Acetobacter pasteurianus

It is already known that kinetic resolution of racemic glycidol (2,3-epoxy- 1-propanol) takes place when Acetobacter pasteurianus oxidizes the compound to glycidic acid (2,3-epoxy-propionic acid) with glycidaldehyde (2,3-epoxy -propanal) proposed to be the transient seen in this conversion. Since inhi bition affects the feasibility of a process based on this conversion in a n egative sense, and the chemical reactivity of glycidaldehyde predicts that it could be the cause for the phenomena observed, it is important to know w hich enzyme(s) oxidise(s) this compound. To study this, rac.- as well as (R )-glycidaldehyde were prepared by chemical synthesis and analytical methods developed for their determination. It appears that purified quinohemoprote in alcohol dehydrogenase (QH-ADH type II), the enzyme responsible for the k inetic resolution of rac.-glycidol, also catalyses the oxidation of glycida ldehyde. In addition, a preparation exhibiting dye-linked aldehyde dehydrog enase activity for acetaldehyde, most probably originating from molybdohemo protein aldehyde dehydrogenase (ALDH), which has been described for other A cetic acid bacteria, oxidised glycidaldehyde as well with a preference for the (R)-enantiomer, the selectivity quantified by an enantiomeric ratio (E) value of 7. From a comparison of the apparent kinetic parameter values of QH-ADH and ALDH, it is concluded that ALDH is mainly responsible for the re moval of glycidaldehyde in conversions of glycidol catalysed by A. pasteuri anus cells. It is shown that the transient observed in rac.-glycidol conver sion by whole cells, is indeed (R)-glycidaldehyde. Since both QH-ADH and AL DH are responsible for vinegar production from ethanol by Acetobacters, gro wth and induction conditions optimal for this process seem also suited to y ield cells with high catalytic performance with respect to kinetic resoluti on of glycidol and prevention of formation of inhibitory concentrations gly cidaldehyde. (C) 2001 Elsevier Science Inc. All rights reserved.