CHARACTERIZATION OF A NOVEL TUNGSTEN-CONTAINING FORMALDEHYDE FERREDOXIN OXIDOREDUCTASE FROM THE HYPERTHERMOPHILIC ARCHAEON, THERMOCOCCUS-LITORALIS - A ROLE FOR TUNGSTEN IN PEPTIDE CATABOLISM

Thermococcus litoralis is a strictly anaerobic archaeon (archaebacteri um) that grows at temperatures up to 98-degrees-C by fermenting peptid es. Its growth is stimulated by tungsten, and a tungsten-containing ir on-sulfur protein that has formaldehyde ferredoxin oxidoreductase (FOR ) activity has been purified. FOR is a homotetramer with a subunit M(r ) of 70,000. It contains approximately four irons, four acid-labile su lfides, and one tungsten atom per subunit. The tungsten appears to be present as a pterin cofactor, and the Fe/S seems to comprise an unusua l [4Fe-4S] cluster that in the reduced state exists in a pH-independen t S = 3/2 form and a pH-dependent S = 1/2 form. FOR catalyzed the oxid ation of C1-C3 aldehydes with a temperature optimum greater-than-or-eq ual-to 90-degrees-C and used T. litoralis ferredoxin as an electron ac ceptor. It did not oxidize aldehyde phosphates, utilize CoASH, or redu ce NAD(P). The N-terminal sequence of FOR shows homology with the tung sto-iron-sulfur aldehyde ferredoxin oxidoreductase previously purified from the saccharolytic, hyperthermophilic archaeon Pyrococcus furiosu s, in which it is proposed to function in a novel pyroglycolytic pathw ay (Mukund, S., and Adams, M. W. W. (1991) J. Biol. Chem. 266, 14208-1 4216). We show here that P. furiosus, which will also grow on peptides , albeit poorly, contains a second aldehyde-oxidizing enzyme analogous to FOR. Similarly, T. litoralis, which utilizes saccharides if limite d for peptides, contains low concentrations of an enzyme analogous to AOR. It is proposed that formaldehyde (apparent K(m), 62 mM) is not th e true substrate for FOR; rather, the enzyme has an as yet unknown rol e in peptide fermentation in hyperthermophilic archaea.