Coenzyme F₄₂₀

Coenzyme F₄₂₀ is a family of coenzymes involved in redox reactions in a number of bacteria and archaea. It is derived from coenzyme F_O (7,8-didemethyl-8-hydroxy-5-deazariboflavin) and differs by having a oligoglutamyl tail attached via a 2-phospho-L-lactate bridge. F₄₂₀ is so named because it is a flavin derivative with an absorption maximum at 420 nm.

F₄₂₀ was originally discovered in methanogenic archaea and in Actinomycetota (especially in Mycobacterium). It is now known to be used also by Cyanobacteria and by soil Proteobacteria, Chloroflexi and Firmicutes. Eukaryotes including the fruit fly Drosophila melanogaster and the algae Ostreococcus tauri also use Coenzyme F_O.

F₄₂₀ is structurally similar to FMN, but catalytically it is similar to NAD and NADP: it has low redox potential and always transfer a hydride. As a result, it is not only a versatile cofactor in biochemical reactions, but also being eyed for potential as an industrial catalyst. Similar to FMN, it has two states: one reduced state, notated as F₄₂₀-H₂, and one oxidized state, written as just F₄₂₀. F_O has largely similar redox properties, but cannot carry an electric charge and as a result probably slowly leaks out of the cellular membrane.

A number of F₄₂₀ molecules, differing by the length of the oligoglutamyl tail, are possible; F₄₂₀-2, for example, refers to the version with two glutamyl units attached. Lengths from 4 to 9 are typical.