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Spectroscopic and Computational Evidence that [FeFe] Hydrogenases Operate Exclusively with CO-Bridged Intermediates

[Image: see text] [FeFe] hydrogenases are extremely active H(2)-converting enzymes. Their mechanism remains highly controversial, in particular, the nature of the one-electron and two-electron reduced intermediates called H(red)H(+) and H(sred)H(+). In one model, the H(red)H(+) and H(sred)H(+) state...

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Detalles Bibliográficos
Autores principales: Birrell, James A., Pelmenschikov, Vladimir, Mishra, Nakul, Wang, Hongxin, Yoda, Yoshitaka, Tamasaku, Kenji, Rauchfuss, Thomas B., Cramer, Stephen P., Lubitz, Wolfgang, DeBeer, Serena
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2019
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6956316/
https://www.ncbi.nlm.nih.gov/pubmed/31820961
http://dx.doi.org/10.1021/jacs.9b09745
Descripción
Sumario:[Image: see text] [FeFe] hydrogenases are extremely active H(2)-converting enzymes. Their mechanism remains highly controversial, in particular, the nature of the one-electron and two-electron reduced intermediates called H(red)H(+) and H(sred)H(+). In one model, the H(red)H(+) and H(sred)H(+) states contain a semibridging CO, while in the other model, the bridging CO is replaced by a bridging hydride. Using low-temperature IR spectroscopy and nuclear resonance vibrational spectroscopy, together with density functional theory calculations, we show that the bridging CO is retained in the H(sred)H(+) and H(red)H(+) states in the [FeFe] hydrogenases from Chlamydomonas reinhardtii and Desulfovibrio desulfuricans, respectively. Furthermore, there is no evidence for a bridging hydride in either state. These results agree with a model of the catalytic cycle in which the H(red)H(+) and H(sred)H(+) states are integral, catalytically competent components. We conclude that proton-coupled electron transfer between the two subclusters is crucial to catalysis and allows these enzymes to operate in a highly efficient and reversible manner.