Every organism, from the simplest to the most complex, requires energy.
Nowadays, there are three main types by which energy can be generated. A novel way that has been discovered is known as electron bifurcation.
Electron bifurcation reaction catalyzes two simultaneous reactions. The bifurcating flavin cofactor (center) accepts two electrons and divides their energy into two separate and energetically distinct one-electron pathways. The departure of the low-energy electron (left) creates a high-energy electron (right) capable of reducing ferredoxin. Both reduced compounds, NADH and ferredoxin, perform crucial downstream processes of their own, but the ferredoxin has higher energy and can be used for more difficult chemical reactions.
Electron bifurcation has been recently recognized as the 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.
Electron bifurcation is a clever means that living things use to better extract energy from their metabolic processes. Electrons in metabolism can be thought of as high energy, low energy, or somewhere in between. Bifurcation takes two intermediate electrons and creates one high- and one low-energy electron. High-energy electrons are needed to perform some difficult chemical reactions. How bifurcation works was a mystery—until now. Scientists studied what happens after the flavin cofactor, a compound containing nitrogen and several six-membered rings which is closely related to the vitamin riboflavin, accepts two intermediate-energy electrons. They found a highly energetic, short-lived flavin intermediate, created after the first electron is sent away. The flavin rapidly channels its energy to the remaining electron, giving it a bump up in energy.
Knowing these details of how flavin-based electron bifurcation works provides important new insights into living organisms. Specifically, the research shows how organisms effectively and efficiently manage the energetic content of chemical bonds, positioning electrons at energies to match the reactions they need to grow and survive. It would be a waste of energy to use high-energy electrons in a reaction that does not require them. Conversely, low-energy electrons won't work in a reaction that demands significant energy input. These results may someday inspire the design of a new class of catalysts for certain industrial processes. Also, they may help guide the re-engineering of microbes to more efficiently produce renewable fuels and chemicals.
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