Incorporation of Molybdenum into the Iron-Molybdenum Cofactor of Nitrogenase

• Published in: The Journal of biological chemistry 1999-05, Vol.274 (22), p.15869-15874
• Main Authors: Allen, Ronda M., Roll, Jon T., Rangaraj, Priya, Shah, Vinod K., Roberts, Gary P., Ludden, Paul W.
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Azotobacter vinelandii; Azotobacter vinelandii - enzymology; Azotobacter vinelandii - genetics; bacterial proteins; Bacterial Proteins - chemistry; binding; Clostridium - enzymology; cofactors; dinitrogenase; iron; Molecular Structure; molybdenum; Molybdenum - chemistry; molybdenum storage protein; Molybdoferredoxin - biosynthesis; Molybdoferredoxin - chemistry; nitrogenase; Nitrogenase - chemistry; Nitrogenase - metabolism; Nucleotides - metabolism; Oxidoreductases; precursors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.274.22.15869

The biosynthesis of the iron-molybdenum cofactor (FeMo-co) of dinitrogenase was investigated using99Mo to follow the incorporation of Mo into precursors. 99Mo label accumulates on dinitrogenase only when all known components of the FeMo-co synthesis system, NifH, NifNE, NifB-cofactor, homocitrate, MgATP, and reductant, are present. Furthermore, 99Mo label accumulates only on the gamma protein, which has been shown to serve as a chaperone/insertase for the maturation of apodinitrogenase when all known components are present. It appears that only completed FeMo-co can accumulate on the gamma protein. Very little FeMo-co synthesis was observed when all known components are used in purified forms, indicating that additional factors are required for optimal FeMo-co synthesis. 99Mo did not accumulate on NifNE under any conditions tested, suggesting that Mo enters the pathway at some other step, although it remains possible that a Mo-containing precursor of FeMo-co that is not sufficiently stable to persist during gel electrophoresis occurs but is not observed. 99Mo accumulates on several unidentified species, which may be the additional components required for FeMo-co synthesis. The molybdenum storage protein was observed and the accumulation of 99Mo on this protein required nucleotide.