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Bias from H-2 cleavage to production and coordination changes at the Ni-Fe active site in the NAD(+)-reducing hydrogenase from Ralstonia eutropha
Zitatschlüssel Loscher2006
Autor Loscher, S. and Burgdorf, T. and Zebger, I. and Hildebrandt, P. and Dau, H. and Friedrich, B. and Haumann, M.
Seiten 11658–11665
Jahr 2006
Journal Biochemistry
Jahrgang 45
Nummer 38
Zusammenfassung The soluble NAD(+)-reducing Ni-Fe hydrogenase (SH) from Ralstonia eutropha H16 is remarkable because it cleaves hydrogen in the presence of dioxygen at a unique Ni-Fe active site (Burgdorf et al. (2005) J. Am. Chem. Soc. 127, 576). By X-ray absorption (XAS), FTIR, and EPR spectroscopy, we monitored the structure and oxidation state of its metal centers during H-2 turnover. In NADH-activated protein, a change occurred from the (CN)O2NiII(mu-S)(2)Fe-II(CN)(3)(CO) site dominant in the wild-type SH to a standard-like S2NiII(mu-S)(2)Fe-II(CN)(2)(CO) site as the prevailing species in a specific mutant protein, HoxH-H16L. The wild-type SH primarily was active in H2 cleavage. The nonstandard reaction mechanism does not involve stable EPR-detectable trivalent Ni oxidation states, namely, the Ni-A,B,C states as observed in standard hydrogenases. In the HoxH-mutant protein H16L, H-2 oxidation was impaired, but H-2 production occurred via a stable Ni-C state (Ni-III-H–Fe-II), suggesting a reaction sequence similar to that of standard hydrogenases. It is proposed that reductive activation by NADH of both wild-type and H16L proteins causes the release of an oxygen species from Ni and is initiated by electron transfer from a [2Fe-2S] cluster in the HoxU subunit that at first becomes reduced by electrons from NADH. Electrons derived from H-2 cleavage, on the other hand, are transferred to NAD(+) via a different pathway involving a [4Fe-4S] cluster in HoxY, which is reducible only in wild-type SH but not in the H16L variant.
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