Formula C42H51N6NiO– 13 | ||
 | ||
F430 is the prosthetic group of the enzyme methyl coenzyme M reductase. This enzyme catalyzes the release of methane in the final step of methanogenesis:
CH3–S–CoM + HS–CoB → CH
4 + CoB–S–S–CoM
It is found only in methanogenic Archaea and anaerobic methanotrophic Archaea.
Corphin in context
Nature uses multiple tetrapyrroles - hemes, chlorophyll, and cobalamin. Of the tetrapyrroles with 5 double bonds, F430 is the most reduced. 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. Ni(II) is too small for the N4 binding site of the corphin, which causes the macrocycle to adopt a ruffled structure. Its structure was deduced by X-ray crystallography and NMR spectroscopy.
F430 occurs in particularly high concentrations in archaea that are thought to be involved in reverse methanogenesis. Organisms that promote this remarkable reaction contain 7% by weight nickel protein.
The biosynthesis of F430 from sirohydrochlorin proceeds via a four steps. The sequence begins with insertion of nickel mediated by a chelatase, similar to that in the biosynthesis of vitamin b12. Subsequent steps include amidation, partial hydrogenation of the pyrrolic backbone, and lactonization.