Nitrogenase Fe-protein

Figure 3-10 Estimation of the molecular mass of the polypeptide chain of the nitrogenase Fe-protein using SDS-poly-acrylamide electrophoresis from a set of four standard curves. The marker proteins are (1) catalase, (2) fumarase, (3) aldolase, (4) glyceraldehyde-phosphate dehydrogenase, (5) a-chymotrypsinogen A, and (6) myoglobin, (o) indicates position of azoferredoxin. From Nakos and Mortenson.195...

The assembly of the molybdenum nitrogenase Fe protein involves the nifH gene and at least the nifS, nifU, and niJM gene prodncts that are implicated in the [4Fe 4S] cluster assembly, while the assembly of MoFe protein requires at least 15 nif gene products and involves the biosynthesis of FeMo cofactor and FeMo cofactor deficient MoFe protein in separate pathways and the insertion of FeMo cofactor into the MoFe protein. 

The [4Fe-4S] cluster found in the nitrogenase Fe-protein component and ferredoxin. 

A) Preliminary x-ray crystal structure of the Azotobacter vinelandii nitrogenase Fe protein. ... 

Whether, this is AMP or not remains to be established. Av2 and Cp2 were relatively free of these compounds. Moreover the uv spectrum of Rr2 contained a shoulder at 269 which was absent from Av2 and Cp2. This evidence, together with the observation that Rr2 and the Fe protein from Azospirillum brasilense require an activating factor (Section II,E), implies that at least two distinct types of nitrogenase Fe proteins exist. 

The epr signal of oxidized A. vinelandii ferredoxin I integrates to two electrons/mol (Sweeney et al., 1975) whereas that of ferredoxin I from M. ftavum integrates to a maximum of only 0.35 electrons/mol (Yates et al., 1978). This may mean that the two 4Fe4S clusters of M. flavum ferredoxin are sufficiently close to interact to diminish the epr signal (cf. nitrogenase Fe protein. Section II,D,5) whereas those of the A. vinelandii ferredoxin are remote. 

The work of Carnahan et al. (1960) established that sodium pyruvate was an electron donor for nitrogen fixation in clostridia and the discovery of ferredoxin stemmed from its role in this reaction (Mortenson, 1%4). In 1974 Walker and Mortenson established that ferredoxin transferred electrons directly from hydrogenase to nitrogenase Fe protein. In this system the sequence of electrons would be... 

---