MOLECULAR-GENETICS OF LACTATE-DEHYDROGENASES FROM LACTIC-ACID BACTERIA

We have cloned 2 D-lactate-dehydrogenase genes (D-LDH) and one D-hydro xy-isocaproate-dehydrogenase gene (D-HicDH) from lactic acid bacteria (Lactobacillus delbrueckii subsp bulgaricus, Pediococcus acidilactici) by complementation of a LDH-negative mutant of Escherichia coli. The sequence of these genes has revealed the existence of a novel family o f NADH-dependent alpha-hydroxy-acid dehydrogenases which were complete ly different from the L-LDH family. The structure-function relationshi ps of enzymes from this new family are currently under study via site- directed mutagenesis.