Cofactor F430

• Coenzyme F430
• Cofactor F430

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The cofactor F430, F430 also, is the prosthetic group of the enzyme methyl -coenzyme M reductase. His absorption maximum at lambda max = 430 nm it owes its name. The cofactor occurs only in methanogenic archaea.

Discovery

F430 was discovered in 1977 by Jean Legall as yellow component in cell extracts of Methanobacterium thermoautotrophicum. Because of its strong absorption at lambda max = 430 nm it was called factor F430. The 1980 proposed by Thauer and coworkers tetrapyrrole -like structure was finally verified by NMR studies.

Occurrence

Although the cofactor F430 in its construction is similar to other tetrapyrroles, it was detected only in methanogenic archaea. In those it serves only as a prosthetic group of the enzyme methyl -coenzyme M reductase (MCR ).

Chemical Properties

F430 remembers its structure for a tetrapyrrole ring and is similar to the porphyrins or corrins. The chromophore is a tetrahydro- derivative of the so-called Corphins. The ring system in F430 has a total of only five double bonds, making it the most reduced tetrapyrrole in nature. Due to the lack of conjugated double bonds, it is in contrast to the more-unsaturated tetrapyrroles ( for example, the red heme ) yellow. In addition, the ring system is increased by two be tied rings.

Yet it is the only descendant of a Tetrapyrrolsystems containing a nickel ion. This is present as Ni ( I), and is paramagnetic. The cofactor can be isolated by denaturing the MCR by means of acids. Isolated F430 is thermally unstable and oxygen sensitive.

Recently, a variant of the cofactor F430 was discovered, which is modified at C172 atom by a methylthio group ( see picture). This variant has but apparently no effect on the nickel atom in the center, which is essential for the function of cofactor. Why this variant is modified, is still under discussion.

Importance

The cofactor is the prosthetic group of the enzyme methyl -coenzyme M reductase (MCR ). Each enzyme contains two non-covalently bound F430. MCR catalyzes the last step of methanogenesis, is released in the methane and a Disulfidkomplex of coenzyme M ( CoM ) and coenzyme B ( CoB ) arises:

The exact mechanism has not been elucidated. It is also unclear whether (III ) can be formed as a result of catalytic Ni.