Function of coenzyme F420-dependent NADP reductase in methanogenic archaea containing an NADP-dependent alcohol dehydrog
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© Springer-Verlag 1997
O R I G I N A L PA P E R
Holger Berk · Rudolf K. Thauer
Function of coenzyme F420-dependent NADP reductase in methanogenic archaea containing an NADP-dependent alcohol dehydrogenase
Received: 12 May 1997 / Accepted: 1 July 1997
Abstract Methanogenic archaea growing on ethanol or isopropanol as the electron donor for CO2 reduction to CH4 contain either an NADP-dependent or a coenzyme F420-dependent alcohol dehydrogenase. We report here that in both groups of methanogens, the N 5, N10-methylenetetrahydromethanopterin dehydrogenase and the N5, N10-methylenetetrahydromethanopterin reductase, two enzymes involved in CO2 reduction to CH4, are specific for F420. This raised the question how F420H2 is regenerated in the methanogens with an NADP-dependent alcohol dehydrogenase. We found that these organisms contain catabolic activities of an enzyme catalyzing the reduction of F420 with NADPH. The F420-dependent NADP reductase from Methanogenium organophilum was purified and characterized. The N-terminal amino acid sequence showed 42% sequence identity to a putative gene product in Methanococcus jannaschii, the total genome of which has recently been sequenced. Key words Coenzyme F420 · F420-dependent NADP reductase · F420-dependent N 5,N10methylenetetrahydromethanopterin dehydrogenase · F420-dependent N 5, N10-methylenetetrahydromethanopterin reductase · Methanogenic archaea · Methanogenium organophilum · Methanobacterium palustre · Methanogenium liminatans · Methanoculleus thermophilicus Abbreviations td Doubling time · F420 Coenzyme F420 · H4 MPT Tetrahydromethanopterin · CH2 = H4 MPT N 5, N10-methylene-H4MPT
H. Berk · R. K. Thauer (Y) Max-Planck-Institut für terrestrische Mikrobiologie, Abteilung Biochemie, Karl-von-Frisch-Strasse, D-35043 Marburg, Germany Tel. +49-6421-178200; Fax +49-6421-178209 e-mail: [email protected] H. Berk · R. K. Thauer Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, D-35043 Marburg, Germany
Introduction Until recently, it was assumed that the process of methane formation in methanogenic archaea does not involve pyridine nucleotides (Wolfe 1991; Weiss and Thauer 1993; Thauer 1997). None of the enzymes involved in methanogenesis from CO2, acetate, or methanol was found to utilize NAD or NADP as coenzyme. Instead, some of the enzymes use the 5-deazaflavin F420 as coenzyme; it functions like NAD(P) by transferring only two electrons with one proton (a hydride ion). The redox potential E′0 of the F420/F420H2 couple is –360 mV as compared to –320 mV for the NAD(P)+/NAD(P)H couple (Walsh 1986; Gloss and Hausinger 1987). Recently, methanogenic archaea that can grow on CO2 and ethanol or isopropanol as sole energy sources have been isolated; CH4 and acetic acid or acetone, respectively, are thereby generated as catabolic end products (Widdel 1986; Zellner and Winter 1987; Widdel et al. 1988). These methanogens have been found to contain either an NADP-dependent alcohol dehydrogenase or an F420-dependent alcohol dehydrogenase (Bleicher et
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