F₄₃₀ is the prosthetic group of the enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 methyl coenzyme M reductase. It is found only in methanogen

Methanogen

Methanogens are microorganisms that produce methane as a metabolic byproduct in anoxic conditions. They are classified as archaea, a group quite distinct from bacteria...

ic Archaea

Archaea

The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...

. This enzyme catalyzes the release of methane in the final step of methanogenesis

Methanogenesis

Methanogenesis or biomethanation is the formation of methane by microbes known as methanogens. Organisms capable of producing methane have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with...

:

+ HS–CoB

Coenzyme B

Coenzyme B is a coenzyme required for redox reactions in methanogens. The full chemical name of coenzyme B is 7-mercaptoheptanoylthreoninephosphate...

  → + CoB–S–S–CoM

Corphin in context

Nature uses multiple tetrapyrrole

Tetrapyrrole

Tetrapyrroles are compounds containing four pyrrole rings. With the exception of corrin, the four pyrrole rings are interconnected through one-carbon bridges, in either a linear or a cyclic fashion...

s - heme

Heme

A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...

s, chlorophyll

Chlorophyll

Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...

, and cobalamin. F₄₃₀ is the most reduced tetrapyrrole in nature with only five double bonds. This particular tetrapyrrole derivative is called a corphin. Because of its relative lack of conjugated unsaturation, it is yellow, not the intense purple-red associated with more unsaturated tetrapyrroles. It is also the only tetrapyrrole derivative found in nature to contain nickel

Nickel

Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

. Ni(II) is too small for the N4 binding site of the corphin, which causes the macrocycle to adopt a ruffled structure.

Proposed mechanism of methanogenesis

The active form of F₄₃₀ contains Ni(I), analogously to the reduced B₁₂ cofactors that feature Co(I). Whereas Co(I) is d⁸ and diamagnetic, Ni(I) is d⁹ and paramagnetic. The mechanism by which Nature cleaves the bond in methyl coenzyme M is presently (2006) unclear although it is known that both coenzyme M and coenzyme B fits into a channel terminated by the axial site on nickel. A plausible mechanism entails electron transfer from Ni(I) (to give Ni(II)), and this electron transfer

Electron transfer

Electron transfer is the process by which an electron moves from an atom or a chemical species to another atom or chemical species...

 initiates formation of . Coupling of the coenzyme M thiyl radical with HS coenzyme B releases a proton and re-reduces Ni(II) by one-electron, regenerating Ni(I).

Its structure was deduced by X-ray crystallography

X-ray crystallography

X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...

 and NMR spectroscopy

NMR spectroscopy

Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a research technique that exploits the magnetic properties of certain atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained...

.

Anaerobic methane oxidation

F430 occurs in very high concentrations in bacteria that are thought to be involved in reverse methanogenesis, where methane is converted to methyl coenzyme M. Organisms that promote this remarkable reaction contain 7% by weight nickel protein.