Electron bifurcation

Abstract

Electron bifurcation is the recently recognized third mechanism of biological energy conservation. It simultaneously couples exergonic and endergonic oxidation-reduction reactions to circumvent thermodynamic barriers and minimize free energy loss. Little is known about the details of how electron bifurcating enzymes function, but specifics are beginning to emerge for several bifurcating enzymes. To date, those characterized contain a collection of redox cofactors including flavins and iron-sulfur clusters. Here we discuss the current understanding of bifurcating enzymes and the mechanistic features required to reversibly partition multiple electrons from a single redox site into exergonic and endergonic electron transfer paths.

Molecular basis of the flavin‐based electron‐bifurcating caffeyl‐CoA reductase reaction

“…The FBEB reaction was started by the addition of 500 lM NADH [7]. The same assay conditions were used for the other redox agents using instead of 20 lM ferredoxin 50 lM FAD, 50 lM FMN, 500 lM dichlorophenol indophenol and 1 mM ferricyanide (K 3 Fe(CN) 6 ). Measurements using the methyl viologen oxidation assay were done as described earlier [7].…”

“…Several FBEB enzymes are functionally characterized to date and recently reviewed . One of them is the FBEB caffeyl‐CoA reductase (CarCDE) which reduces 1 caffeyl‐CoA to hydrocaffeyl‐CoA ( ≈ +33 to −10 mV; based on the fumarate/succinate or crotonyl‐CoA/butyryl‐CoA couples) and 2 Fd ox to 2 ( ~ −450 to −500 mV) at the expense of 2 NADH ( = −320 mV) which are oxidized to 2 NAD + (Fig.…”

Sweating the assets of flavin cofactors: new insight of chemical versatility from knowledge of structure and mechanism

“…These are rehearsed in some detail elsewhere, and are therefore not the focus of this article. Likewise, the versatility of flavins in 'nonchemical' transformations that is in photochemistry/light sensing [8] or long-range electron transfer (in selected cases involving complex bifurcation mechanisms [9,10]), has also been reviewed elsewhere. The purpose here is not to recapitulate this familiar territory.…”

Ligand binding and conformational dynamics in a flavin‐based electron‐bifurcating enzyme complex revealed by Hydrogen–Deuterium Exchange Mass Spectrometry

“…Energy coupling is achieved by driving an endergonic redox reaction using an exergonic redox reaction. Both reactions share the same electron donor, ferredoxin, as low-potential electron acceptor and a flavin as the site for electron bifurcation [1][2][3][4][5]. FBEB plays a pivotal role in diverse anaerobic bacteria and archaea that perform ecologically important processes such as methanogenesis [6], acetogenesis [7], and fermentation [8].One of the architecturally most-simple FBEB enzyme complexes is the NADH-dependent reduced ferredoxin: NADP + oxidoreductase (NfnAB).…”