"Bifurcation d'électron" ?

[Geb]

Bonjour,

J'ai lu il y a 3 jours une publication récente disponible gratuitement sur PubMed :

The ineluctable requirement for the trans-iron elements molybdenum and/or tungsten in the origin of life (2012)

En page 5 du pdf, il est écrit :

As detailed in references 17 and 18, several 2-electron compounds under certain circumstances feature so-called crossed-over individual redox transitions which allows them to redox bifurcate electrons with one of the two reducing equivalents going seemingly uphill towards very low potential electron acceptors.

Comme le titre de cette discussion l'indique, c'est le mécanisme de bifurcation des électrons que je voudrais que l'on m'explique. La référence 18 de ce papier est ici :

Redox bifurcations: Mechanisms and importance to life now, and at its origin (2012)

J'ai cherché une publication qui mentionnait ce mécanisme dans son titre et j'ai trouvé celle-ci :

Hydrogen, metals, bifurcating electrons, and proton gradients: The early evolution of biological energy conservation (2012)

Dans le résumé :

Electron bifurcation is a newly recognized cytosolic process that anaerobes use generate low potential electrons, it plays an important role in some forms of methanogenesis and, via speculation, possibly in acetogenesis. Electron bifurcation likely figures into the early evolution of biological energy conservation.

Puisqu'un papier de 2012 parle de quelque chose de nouveau, j'ai cherché le premier papier qui en parlait et je suis tombé là-dessus :

Large scale domain movement in cytochrome bc1: a new device for electron transfer in proteins (2001)

Donc, 2001 ce serait effectivement très neuf. Quelqu'un a-t-il une petite idée de ce dont il s'agit ?

Cordialement.
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[Geb]

Bonjour,

J'ai lu il y a 3 jours une publication récente disponible gratuitement sur PubMed :

The ineluctable requirement for the trans-iron elements molybdenum and/or tungsten in the origin of life (2012)

Je viens de trouver un article de presse sur le site de la revue Scientific American qui traite de cette publication scientifique :

A Spoonful of Molybdenum, some Ulysses and the Origin of Life

Voilà ce qu'il est dit à propos de la fameuse bifurcation d'électron :

Inevitable. Essential. Unavoidable. Words rarely used to describe molybdenum. Why, of all obscure elements known to man, would molybdenum be necessary for life?

The answer lies with the electrons that whirl around the molybdenum core. Like many other metals, molybdenum is eager to take an extra electron under its wings or give a spare one away. Life has eagerly exploited this ability to juggle electrons around. Cells not only incorporate molybdenum ions into their enzymes, but also zinc, copper, iron and nickel. Many of these metal containing proteins shuttle electrons between molecules, as if they are playing a massive game of hot potato, changing, breaking and building molecules along the way. Electrons truly are what makes life go round. Or, as the Hungarian Nobel prize winner Albert Szent-Györgyi put it: “Life is nothing but an electron looking for a place to rest”.

Some electrons find cold and empty beds in their search. Take the methanogens. These bacteria and archaea make a living by stripping electrons from hydrogen (H₂) and attaching them onto carbon dioxide (CO₂) in several steps, generating methane (CH₄) and water (H₂O) in the process. That might sound easy enough, but carbon dioxide is not a thankful molecule: it’s stable as it is, and very reluctant to accept additional electrons.

This is where molybdenum comes in. Or rather could come in, for while molybdenum plays a role in the conversion of carbon dioxide to methane, the mechanism that Russell proposes has not yet been proven for this particular reaction. Russell’s argument boils down to a single point: molybdenum can ease difficult electron transfers because it usually has not one, but two electrons to give away. There’s nothing stopping molybdenum from donating these electrons to two different molecules. In this way, the molybdenum ion could compensate for the effort of imposing one electron onto a stubborn naysayer (such as carbon dioxide), by donating the other one to a more willing recipient.

The forking of electrons works because the electron that rolls ‘downhill’ releases energy that is channelled into pushing the other electron ‘up the slope’. Some molybdenum enzymes are known to perform this trick, but no one really knows how widespread such crossed electron transfers really are in biochemistry. In an article published last year, Russell and Wolfgang Nitschke write that electron bifurcation ‘is an old, but almost forgotten friend of research’.

Quelqu'un pourrait-il vulgariser cet article de vulgarisation pour moi ?

Le papier cite notamment un article à propos de la "bifurcation d'électrons" en ces mots : "Some molybdenum enzymes are known to perform this trick". L'article est ici :

Electrochemical studies of arsenite oxidase: an unusual example of a highly cooperative two-electron molybdenum center. (Hoke et al., 2004)

Cordialement.

Cordialement.

[Geb]

Bonjour,

Grâce à l'aide du Dr Michael Russell, j'ai trouvé d'autres papiers qui discutent justement de cette notion de "bifurcation d'électrons" :

- Energy Conservation via Electron-Transferring Flavoprotein in Anaerobic Bacteria (Herrmann et al., 2008)

- Coupled Ferredoxin and Crotonyl Coenzyme A (CoA) Reduction with NADH Catalyzed by the Butyryl-CoA Dehydrogenase/Etf Complex from Clostridium kluyveri (Li et al., 2008)

- Methanogenic archaea: ecologically relevant differences in energy conservation (Thauer et al., 2008)

- Coupling of ferredoxin and heterodisulfide reduction via electron bifurcation in hydrogenotrophic methanogenic Archaea (Kaster et al., 2011)

De belles lectures en perspective, lorsque j'aurai un peu de temps à y consacrer.

Cordialement.