| Autor: |
Camprubi E; Department of Genetics, Evolution and Environment, University College London, London, UK., Jordan SF; Department of Genetics, Evolution and Environment, University College London, London, UK., Vasiliadou R; Department of Genetics, Evolution and Environment, University College London, London, UK., Lane N; Department of Genetics, Evolution and Environment, University College London, London, UK. |
| Jazyk: |
angličtina |
| Zdroj: |
IUBMB life [IUBMB Life] 2017 Jun; Vol. 69 (6), pp. 373-381. Date of Electronic Publication: 2017 May 03. |
| DOI: |
10.1002/iub.1632 |
| Abstrakt: |
Iron-sulphur proteins are ancient and drive fundamental processes in cells, notably electron transfer and CO 2 fixation. Iron-sulphur minerals with equivalent structures could have played a key role in the origin of life. However, the 'iron-sulphur world' hypothesis has had a mixed reception, with questions raised especially about the feasibility of a pyrites-pulled reverse Krebs cycle. Phylogenetics suggests that the earliest cells drove carbon and energy metabolism via the acetyl CoA pathway, which is also replete in Fe(Ni)S proteins. Deep differences between bacteria and archaea in this pathway obscure the ancestral state. These differences make sense if early cells depended on natural proton gradients in alkaline hydrothermal vents. If so, the acetyl CoA pathway diverged with the origins of active ion pumping, and ancestral CO 2 fixation might have been equivalent to methanogens, which depend on a membrane-bound NiFe hydrogenase, energy converting hydrogenase. This uses the proton-motive force to reduce ferredoxin, thence CO 2 . The mechanism suggests that pH could modulate reduction potential at the active site of the enzyme, facilitating the difficult reduction of CO 2 by H 2 . This mechanism could be generalised under abiotic conditions so that steep pH differences across semi-conducting Fe(Ni)S barriers drives not just the first steps of CO 2 fixation to C1 and C2 organics such as CO, CH 3 SH and CH 3 COSH, but a series of similar carbonylation and hydrogenation reactions to form longer chain carboxylic acids such as pyruvate, oxaloacetate and α-ketoglutarate, as in the incomplete reverse Krebs cycle found in methanogens. We suggest that the closure of a complete reverse Krebs cycle, by regenerating acetyl CoA directly, displaced the acetyl CoA pathway from many modern groups. A later reliance on acetyl CoA and ATP eliminated the need for the proton-motive force to drive most steps of the reverse Krebs cycle. © 2017 IUBMB Life, 69(6):373-381, 2017.
(© 2017 The Authors IUBMB Life published by Wiley Periodicals, Inc. on behalf of International Union of Biochemistry and Molecular Biology.) |
| Databáze: |
MEDLINE |
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