title: A study of one of the iron-sulphur clusters in oxidized hydrogenase from Megasphaera elsdenii by magnetic-circular-dichroism spectroscopy.
abstract: The m.c.d. spectrum of the oxidized state of hydrogenase from Megasphaera elsdenii has been measured at liquid-helium temperatures. This oxidation state of the enzyme displays a characteristic rhombic e.p.r. signal with g-values of 2.101, 2.052 and 2.005 assigned previously to a [4Fe-4S]3+ cluster as in oxidized HiPIP (high-potential iron-sulphur protein) [Van Dijk, Grande, Mayhew & Veeger (1980) Eur. J. Biochem. 107, 251-261]. The low-temperature m.c.d. spectrum shows no features attributable to an oxidized four-iron cluster of the HiPIP type, but does reveal broad, positive peaks at 460 and 730 nm, which magnetize in a manner untypical of a spin S = 1/2 cluster with g-values close to 2. The m.c.d. spectrum is most closely similar to that of dye-oxidized P-clusters known in the enzyme nitrogenase. It is therefore proposed that the rhombic e.p.r. spectrum at a g-value close to 2 arises from an m.c.d.-silent radical species that may be related chemically to the cysteine persulphide species, RS-S., recently found in the hexacyanoferrate-oxidized seven-iron ferredoxin of Azotobacter vinelandii [Morgan, Stephens, Devlin, Stout, Melis & Burgess (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 1931-1935].
authors.forename: A J
authors.initials: AJ
authors.lastname: Thomson
authors.forename: S J
authors.initials: SJ
authors.lastname: George
authors.forename: A J
authors.initials: AJ
authors.lastname: Richards
authors.forename: A E
authors.initials: AE
authors.lastname: Robinson
authors.forename: H J
authors.initials: HJ
authors.lastname: Grande
authors.forename: C
authors.initials: C
authors.lastname: Veeger
authors.forename: C
authors.initials: C
authors.lastname: Van Dijk
mesh_terms: D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy; D006864:Hydrogenase; D007506:Iron-Sulfur Proteins / Q000032:analysis*; D008667:Metalloproteins / Q000032:analysis*; D010084:Oxidation-Reduction; D045854:Veillonellaceae / Q000201:enzymology*
chemical_list: D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D006864:Hydrogenase