Re‐Face Specificity at C14a of Methylenetetrahydromethanopterin and Si‐Face Specificity at C5 of Coenzyme F₄₂₀ for Coenzyme F₄₂₀‐Dependent Methylenetetrahydromethanopterin Dehydrogenase from Methanogenic Archaea

Abstract

Coenzyme F,,,-dependent methylenetetrahydromethanopterin dehydrogenase from methanogenic Archaea catalyzes the reversible transfer of a hydride ion from C14a of N5,Mo-methylenetetrahydromethanopterin to C5 of coenzyme F,,,. In this study, we report that this hydride transfer proceeds stereospecifically from the Re face at C14a to the Si face at C5. The results were obtained by using chirally 3H-labelled N5,Mo-methylenetetrahydromethanopterin generated via Re-face-specific H,-forming N5,Wo-methylenetetrahydromethanopterin dehydrogenase and by analyzing reduced coenzyme F,,, via Si-face-specific F,,,-reducing hydrogenase.Keywords. Coenzyme F,,, ; stereospecificity ; methylenetetrahydromethanopterin dehydrogenase ; hydrogenase.Coenzyme F4,,-dependent methylene tetrahydromethanopterin dehydrogenase catalyzes the reversible conversion of N5,Mo-methylenetetrahydromethanopterin (CH,=H,MPT) and coenzyme F,,, (F,,,) to W,Mo-methenyl-H,MPT (CH= H4MPT+) and reduced coenzyme F,,, (F4zoH,) (reaction a; for structures of CH,=H,MPT, CH=KMPT+, F,,, and F42, HZ see The enzyme is found in methanogenic Archaea (Schworer and Thauer, 1991) and Archaeoglobus species (Moller-Zinkhan et al., 1989;Vorholt et al., 1994 on lactate plus sulfate, the enzyme catalyzes the oxidation of CH,=H,MPT to CH-H,MPT+ as an intermediary step in CO, formation (Keltjens and Vogels, 1993; Thauer and Kunow, 1995).

Regulation of the synthesis of H 2 -forming methylenetetrahydromethanopterin dehydrogenase (Hmd) and of HmdII and HmdIII in Methanothermobacter marburgensis

“…From in vitro studies it was known that, in the presence of methenyl-H 4 MPT + , Hmd together with Mtd can catalyze the reduction of F 420 with H 2 (Von Bünau et al 1991;Klein and Thauer 1995). The two enzymes together thus could substitute for Frh in vivo in catalyzing reaction 2.…”

Function of H 2 -forming methylenetetrahydromethanopterin dehydrogenase from Methanobacterium thermoautotrophicum in coenzyme F 420 reduction with H 2

“…This enzyme has been found in all methanogens capable of growth on H 2 and CO 2 and investigated in this respect (Vaupel and Thauer 1997). Besides the F 420 -reducing hydrogenase, many methanogenic archaea contain two other enzymes that together in vitro can also catalyze the reduction of F 420 with H 2 (Klein and Thauer 1995). These are the H 2 -forming methylenetetrahydromethanopterin dehydrogenase (Hmd) and the F 420 -dependent methylenetetrahydromethanopterin dehydrogenase (Mtd).…”

Physiology, Biochemistry, and Applications of F420- and Fo-Dependent Redox Reactions

“…11) (166). The reaction is catalyzed through a ternary complex mechanism (276,284), wherein hydride transfer occurs between C-14a of methylene-H 4 MPT (Re-face stereospecific) and C-5 of F 420 H 2 (Si-face stereospecific) (166, [287][288][289]. Crystal structures of Mer homologs have been solved from three organisms, Methanoplanus kandleri (159), Methanothermobacter marburgensis (159), and Methanosarcina barkeri (48).…”