SI-FACE STEREOSPECIFICITY AT C5 OF COENZYME-F420 FOR F420-DEPENDENT N5,N-10-METHYLENETETRAHYDROMETHANOPTERIN DEHYDROGENASE, F420-DEPENDENT N5,N-10-METHYLENETETRAHYDROMETHANOPTERIN REDUCTASE AND F420H2-DIMETHYLNAPHTHOQUINONE OXIDOREDUCTASE

Coenzyme F420-dependent enzymes catalyze the reversible reduction of F420 by stereospecific hydride transfer to C5 of 5-deazaflavin. Two F420-dependent enzymes have been investigated with respect to the stereochemistry of hydride transfer, the F420-dependent NADP reductase and the F420-reducing hydrogenase. Both enzymes were found to be Si-face specific. In this study we report that three additional F420-dependent enzymes are also Si-face specific: N5,N-10-methylenetetrahydromethanopterin dehydrogenase, N5,N-10-methylenetetrahydromethanopterin reductase and coenzyme F420H2: dimethylnaphthoquinone oxidoreductase (F420H2 dehydrogenase). Thus, all five characterized F420-dependent enzymes are Si-face specific, which is noteworthy since coenzyme F420 is functionally similar to pyridine nucleotides and both Si-face specific and Re-face specific pyridine-nucleotide-dependent enzymes exist.