Stereochemistry and mechanism of hydrogen transfer between NADPH and methylenetetrahydrofolate in the reaction catalyzed by methylenetetrahydrofolate reductase from pig liver

Si‐face stereospecificity at C5 of coenzyme F420 for F420‐dependent N5,N10‐methylenetetrahydromethanopterin dehydrogenase, F420‐dependent N5,N10‐methylenetetrahydromethanopterin reductase and F420H2:dimethylnaphthoquinone oxidoreductase

“…Some of these enzymes have been shown to be Si-face specific and some Re-face specific (Sumner and Matthews, 1992). This finding cannot be taken as indicative of the existence of both Si-face and Re-face specific F,,,-dependent enzymes.…”

“…The NADP-dependent methylenetetrahydrofolate reductase has been shown to be Si-face specific at C4 of the pyridine nucleotide (Sumner and Matthews, 1992); in contrast, the NADP-dependent methylenetetrahydrofolate dehydrogenase exhibits Re-face specificity (Ramasastri and Blakley, 1964).…”

Si‐Face Stereospecificity at C5 of Coenzyme F420 for F420‐Dependent Glucose‐6‐Phosphate Dehydrogenase from Mycobacterium smegmatis and F420‐Dependent Alcohol Dehydrogenase from Methanoculleus thermophilicus

“…(a) Flavoproteins are known to catalyze the reduction of synthetic 8-hydroxy-5-deaza-FAD. Some of these enzymes have been shown to be Si-face-stereospecific with respect to C5 of the synthetic deazaflavin and others to be Re-face-stereospecific (Sumner and Matthews, 1992). (b) The amino acid sequence of four of the eight F,,,,-dependent enzymes analyzed for stereospecificity are known (Shuber et al, 1986;Alex et a]., 1990;Mukhopadhyay et al, 1995;Vaupel and Thauer, 1995).…”

Characterization of NADP+ binding to perdeuterated MurB: backbone atom NMR assignments and chemical-shift changes

“…Assuming direct hydride transfer, this positioning of NADP (and, by inference, NADPH) must result in hydride transfer to the si face of the FAD isoalloxazine ring. Hydride transfer to the si face has been observed for only one other¯avoenzyme (Sumner & Matthews, 1992).…”

“…The third proposed site (Benson et al, 1995) would result in a hydride transfer to the re face. Hydride transfer to the si face is apparently quite uncommon: with one known exception (Sumner & Matthews, 1992), hydride transfer from NADPH to enzyme-bound FAD takes place on the re face of the isoalloxazine ring (Manstein et al, 1986;Ghisla & Massey, 1989). Moreover, for NADPH to bind to the third site would require at least two structural changes to occur within MurB: signi®cant movement of the loop containing P111, and rearrangement of the ribityl moiety of the FAD.…”