title: The exchange activities of [Fe] hydrogenase (iron-sulfur-cluster-free hydrogenase) from methanogenic archaea in comparison with the exchange activities of [FeFe] and [NiFe] hydrogenases.
abstract: [Fe] hydrogenase (iron-sulfur-cluster-free hydrogenase) catalyzes the reversible reduction of methenyltetrahydromethanopterin (methenyl-H4MPT+) with H2 to methylene-H4MPT, a reaction involved in methanogenesis from H2 and CO2 in many methanogenic archaea. The enzyme harbors an iron-containing cofactor, in which a low-spin iron is complexed by a pyridone, two CO and a cysteine sulfur. [Fe] hydrogenase is thus similar to [NiFe] and [FeFe] hydrogenases, in which a low-spin iron carbonyl complex, albeit in a dinuclear metal center, is also involved in H2 activation. Like the [NiFe] and [FeFe] hydrogenases, [Fe] hydrogenase catalyzes an active exchange of H2 with protons of water; however, this activity is dependent on the presence of the hydride-accepting methenyl-H4MPT+. In its absence the exchange activity is only 0.01% of that in its presence. The residual activity has been attributed to the presence of traces of methenyl-H4MPT+ in the enzyme preparations, but it could also reflect a weak binding of H2 to the iron in the absence of methenyl-H4MPT+. To test this we reinvestigated the exchange activity with [Fe] hydrogenase reconstituted from apoprotein heterologously produced in Escherichia coli and highly purified iron-containing cofactor and found that in the absence of added methenyl-H4MPT+ the exchange activity was below the detection limit of the tritium method employed (0.1 nmol min(-1) mg(-1)). The finding reiterates that for H2 activation by [Fe] hydrogenase the presence of the hydride-accepting methenyl-H4MPT+ is essentially required. This differentiates [Fe] hydrogenase from [FeFe] and [NiFe] hydrogenases, which actively catalyze H2/H2O exchange in the absence of exogenous electron acceptors.
authors.affiliation: Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Strasse, 35043, Marburg, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Vogt
authors.forename: Erica J
authors.initials: EJ
authors.lastname: Lyon
authors.forename: Seigo
authors.initials: S
authors.lastname: Shima
authors.forename: Rudolf K
authors.initials: RK
authors.lastname: Thauer
mesh_terms: D001105:Archaea / Q000201:enzymology*; D002384:Catalysis; D006864:Hydrogenase / Q000302:isolation & purification / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000302:isolation & purification / Q000378:metabolism*; D013058:Mass Spectrometry; D012680:Sensitivity and Specificity
chemical_list: D007506:Iron-Sulfur Proteins; C118830:iron hydrogenase; C043296:nickel-iron hydrogenase; D006864:Hydrogenase