Identification of Lactaldehyde Dehydrogenase in Methanocaldococcus jannaschii and Its Involvement in Production of Lactate for F 420 Biosynthesis

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Abstract
One of the early steps in the biosynthesis of coenzyme F 420 in Methanocaldococcus jannaschii requires generation of 2-phospho- l -lactate, which is formed by the phosphorylation of l -lactate. Preliminary studies had shown that l -lactate in M. jannaschii is not derived from pyruvate, and thus an alternate pathway(s) for its formation was examined. Here we report that l -lactate is formed by the NAD + -dependent oxidation of l -lactaldehyde by the MJ1411 gene product. The lactaldehyde, in turn, was found to be generated either by the NAD(P)H reduction of methylglyoxal or by the aldol cleavage of fuculose-1-phosphate by fuculose-1-phosphate aldolase, the MJ1418 gene product.