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J Bacteriol, March 1998, p. 1023-1029, Vol. 180, No. 5
Institut für Biologie,
Humboldt-Universität zu Berlin, D-10115 Berlin, Germany
Received 22 September 1997/Accepted 23 December 1997
The cytoplasmic, NAD-reducing hydrogenase (SH) of Alcaligenes
eutrophus H16 is a heterotetrameric enzyme which contains several cofactors and undergoes a complex maturation during biogenesis. HoxH is
the Ni-carrying subunit, and together with HoxY it forms the
hydrogenase dimer. HoxF and HoxU represent the flavin-containing diaphorase moiety, which is closely related to NADH:ubiquinone oxidoreductase and mediates NADH oxidation. A variety of mutations were
introduced into the four SH structural genes to obtain mutant enzymes
composed of monomeric and dimeric forms. A deletion removing most of
hoxF, hoxU, and hoxY led to the
expression of a HoxH monomer derivative which was proteolytically
processed at the C terminus like the wild-type polypeptide. While the
hydrogenase dimer, produced by a strain deleted of hoxF and
hoxU, displayed H2-dependent dye-reducing activity, the monomeric form did not mediate the activation of H2, although nickel was incorporated into HoxH. Deletion of
hoxH and hoxY led to the production of HoxFU
dimers which displayed NADH:oxidoreductase activity. Mixing the
hydrogenase and the diaphorase moieties in vitro reconstituted the
structure and catalytic function of the SH holoenzyme.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Subforms and In Vitro Reconstitution of the
NAD-Reducing Hydrogenase of Alcaligenes eutrophus
*
Corresponding author. Mailing address: Institut
für Biologie, Humboldt-Universität zu Berlin, Chausseestr.
117, D-10115 Berlin, Germany. Phone: 49-30-20938100. Fax:
49-30-20938102. E-mail: baerbel=friedrich{at}rz.hu-berlin.de.
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