Hydrolysis and reduction of factor 390 by cell extracts of Methanobacterium thermoautotrophicum (strain delta H)

Abstract

Cell extracts of Methanobacterium thermoautotrophicum (strain AH) were found to perform a hydrogendependent reduction of factor 390 (F390), the 8-adenylyl derivative of coenzyme F420. Upon resolution of cell extracts, F390-reducing activity copurified with the coenzyme F420-dependent hydrogenase. This Methanogenic bacteria constitute a group of strictly anaerobic microorganisms that obtain their energy for biosynthesis of carbon in the cell from the conversion of onecarbon substrates or acetate to CH4. During the last decade, several novel coenzymes have been isolated and shown to participate in the methanogenic pathway (11,17). A few years ago, this list of mostly unique compounds became expanded with the discovery of two chromophores showing absorbance maxima at 390 nm (8). These compounds were identified as derivatives of coenzyme F420 (an 8-hydroxy-5-deazaflavin) in which AMP or GMP is linked to the deazaflavin via the 8-hydroxy position and are therefore named factor 390 (F390)-A and F390-G (Fig. 1) (8). These chromophores could be isolated only when growing cultures of Methanobacterium thermoautotrophicum were exposed to oxygen (7,8,16). Subsequent removal of oxygen from the gas phase resulted in the disappearance of the F390 compounds with the concomitant formation of coenzyme F420 (7, 16).Recently, enzymatic synthesis of F390 was demonstrated to occur in cell extracts of the organism (13). The reaction used oxidized coenzyme F420 and ATP as substrates and proceeded only when the extracts had been pretreated with oxygen. The ability to synthesize F390 was rapidly but reversibly lost when the extracts were brought under reducing conditions (13).In order to ascribe a physiological role to factor(s) F390, the potential for interconversion of this compound(s) in cell extracts was further examined. In this article, we report the H2-dependent reduction of F390-A and its enzymatic hydrolysis to coenzyme F420 by cell extracts of M. thermoautotrophicum. Optimal conditions for the F390-reducing activity and F390 hydrolase are described and compared with those of the coenzyme F420-reducing hydrogenase and the

Growth phase-dependent transcription of the genes that encode the two methyl coenzyme M reductase isoenzymes and N5-methyltetrahydromethanopterin:coenzyme M methyltransferase in Methanobacterium thermoautotrophicum delta H

“…Another possibility is that H2 limitation leads to the synthesis of a specific signal compound, analogous to cyclic AMP in the lac system. One candidate would be factor F390 (16). This compound is synthesized directly from cofactor F420 and could be synthesized in a manner that reflects the intracellular level of reduced versus oxidized cofactor F420.…”

Two-membered mixed cultures of methanogenic and aerobic bacteria in O2-limited chemostats

“…They contain high concentrations of 0,-labile compounds and require a relatively low redox potential for growth (Mah & Smith, 1981 ;Morris, 1976;Vogels et al, 1988). Although methanogens may possess some enzymic self-defence against 0,-toxicity, growth in pure cultures is completely blocked in the presence of 0, (Jones et al, 1983;Kengen et al, 1991;Kiener et al, 1988;Kiener & Leisinger, 1983;Kirby et al, 1981;Patel et al, 1984;Roberton & Wolfe, 1970;Smith & Hungate, 1958;Zehnder & Wuhrmann, 1977). Accordingly, the typical natural habitats of methanogens are environments containing relatively large anoxic areas, such as aquatic sediments, flooded soils, landfills, stratified waters and the intestinal tract of animals.…”

Coenzyme F390 synthetase from Methanobacterium thermoautotrophicum Marburg belongs to the superfamily of adenylate-forming enzymes

“…It may be worthwhile to mention that M. thermoautotrophicum contains a second enzyme in coenzyme F 390 metabolism which hydrolyzes the AMP-coenzyme F 420 bond (13). In this enzyme, coenzyme F 390 hydrolase, a redox-sensitive SH group is involved in catalysis (13,34). It is tempting to speculate that the hydrolase harbors the LGGXS consensus sequence and that coenzyme F 390 synthetase and hydrolase evolved from a single enzyme that catalyzed both reactions.…”

“…Yet, it is most similar to members of the first family. It may be worthwhile to mention that M. thermoautotrophicum contains a second enzyme in coenzyme F 390 metabolism which hydrolyzes the AMP-coenzyme F 420 bond (13). In this enzyme, coenzyme F 390 hydrolase, a redox-sensitive SH group is involved in catalysis (13,34).…”

“…1) (7,32). After the reestablishment of anaerobic conditions, coenzyme F 390 was reconverted into coenzyme F 420 and AMP (13,16). Studies with cell extracts from Methanobacterium thermoautotrophicum ⌬H showed that the formation and degradation of coenzyme F 390 were catalyzed by two separate enzymes, coenzyme F 390 synthetase and coenzyme F 390 hydrolase (12)(13)(14).…”