Biocatalytic racemization of α-hydroxycarboxylic acids using a stereo-complementary pair of α-hydroxycarboxylic acid dehydrogenases

Biocatalytic racemization of aliphatic, (aryl)aliphatic and aromatic alpha-hydroxycarboxylic acids was achieved via a reversible oxidation-reduction sequence using a pair of stereo-complementary Prelog- and anti-Prelog D- and L-alpha-hydroxyisocaproate dehydrogenases from Lactobacillus confusus DSM 20196 and Lactobacillus paracasei DSM 20008, resp., overexpressed in Escherichia coli. The mild reaction conditions ensured essential 'clean' isomerization, undesired 'over-oxidation' of the substrate forming the alpha-ketoacid could be suppressed by exclusion of O-2 and adjustment of the NAD(+)/NADH-ratio. (C) 2009 Elsevier Ltd. All rights reserved.