Molybdopterin cofactor from Methanobacterium formicicum formate dehydrogenase

Area of Science:

• Biochemistry
• Enzymology
• Microbial Metabolism

Background:

• Formate dehydrogenase is a crucial enzyme in microbial metabolism.
• Molybdopterin cofactors are essential for the function of many molybdoenzymes.
• Understanding cofactor structure is key to elucidating enzyme mechanisms.

Purpose of the Study:

• To isolate and characterize the molybdopterin cofactor from Methanobacterium formicicum formate dehydrogenase.
• To determine the structural features of this specific molybdopterin cofactor.
• To assess its functional activity in complementing other enzymes.

Main Methods:

• Enzyme denaturation using guanidine and acid.
• Cofactor isolation under anaerobic conditions.
• Spectroscopic analysis (fluorescence).
• Chemical oxidation and product identification (pterin-6-carboxylic acid).
• Functional complementation assay using a mutant enzyme.

Main Results:

• The molybdopterin cofactor was successfully released from formate dehydrogenase.
• The isolated cofactor exhibited fluorescence upon air exposure, characteristic of molybdopterin cofactors.
• Alkaline permanganate oxidation yielded pterin-6-carboxylic acid, indicating a 6-alkyl side chain of unknown structure.
• The cofactor contained covalently bound phosphate.
• It failed to complement the cofactor-deficient nitrate reductase (nit-1 mutant).

Conclusions:

• The formate dehydrogenase of Methanobacterium formicicum contains a molybdopterin cofactor with a pterin nucleus, a 6-alkyl side chain, and phosphate.
• The cofactor's structure, while related to other molybdopterin cofactors, may possess unique features.
• The cofactor's inability to complement nit-1 suggests specific structural or functional differences compared to other known molybdopterin cofactors.