Of nitrogenase proteins

Additionally, Wang and Watt have shown that the FeMo protein alone can act as an uptake hvdrogenase(63). Specifically, H2 in the presence of [FeMo] causes the reduction of oxidizing dyes such as methylene blue or dichlorophenolindophenol in the absence of Fe protein. The hydrogen evolution and uptake behavior of nitrogenase proteins forces us to consider the ways in which hydrogen can interact with transition metal sulfur centers. This we discuss in the following section. 

Activity of the nitrogenase complex is determined genetically. Taking into account that the content of nitrogenase proteins in Rb. capsulatus can reach 40% of cell protein (Jouanneau et al., 1985), we can conclude that an increase of nitrogenase content in cells by superexpression is not a way for acceleration of specific rate of H2 production by purple bacteria. 

Studies of nitrogenase proteins from the bacteria Azoto-bacter vinelandii and Clostridium pasteurianum have provided structural details of the proteins involved. Two metalloproteins make up the nitrogenase system an Fe... 

Puriflcation of Nitrogenase Proteins from Various Sources... 

Studies of nitrogenase proteins from the bacteria Azoto-bacter vinelandii and Clostridium pasteurianum have provided structural details of the proteins involved. Two metalloproteins make up the nitrogenase system an Fe protein which couples the hydrolysis of ATP to electron transfer, and an FeMo protein which is responsible for binding N2. The dual role of these proteins can be summarized in three steps ... 

B.E. Smith, G. Lang, Mossbauer spectroscopy of nitrogenase proteins from Klebsiella pneumoniae—structural assignments and mechanistic conclusions, Biochem. J. 1974, 137(2), 169-180. 

The nitrogenase system reduces hundreds of millions of kilograms of nitrogen gas to ammonia each year, catalysing tire reaction at ambient temperatures and atmospheric pressure. Nitrogenase consists of two proteins tliat contain... 

These studies of protein-bound heterometallic cubanes have amply demonstrated that the heterometal site is redox active and able to bind small molecules. Although they have yet to be identified as intrinsic components of any protein or enzyme (except as part of the nitrogenase FeMo cofactor cluster (254)), they are clearly attractive candidates for the active sites of redox enzymes. 

The nitrogenase proteins are generally characterized by two letters indicating the species and strains of bacteria and the numerals 1 for the MoFe protein and 2 for the Fe protein. Thus, the Fe protein from Azotobacter vinelandii is Av2 and the MoFe protein from Klebsiella pneumoniae is Kpl. 

In general there are few reproducible data on binding of reducible substrates to the isolated MoFe proteins. However, the S = EPR signal from the FeMoco centers of Kpl is pH dependent, the g values changing with a pKa of 8.7 (50). Of course, the proton is a substrate of nitrogenase however, there is no direct evidence for the proton associated with the pKa being bound directly to FeMoco. Nevertheless, this pKa can be perturbed by addition of the analog substrate acety-... 

Part 1 of the nitrogenase protein contains another interconnected group of Fe-S atoms, this one with eight iron atoms and seven sulfur atoms. This [8Fe-7S] group collects electrons and transmits them to the binding center. Part 2 of nitrogenase contains a third Fe-S group, this one made up of four iron atoms and four sulfur atoms. This part of the enzyme also binds two molecules of ATP. 

NIS measurements have been performed on the rubredoxin (FeSa) type mutant Rm 2-A from Pyrococcus abyssi [103], on Pyrococcus furiosus rubredoxin [104], on Fe2S2 - and Fe4S4 - proteins and model compounds [105, 106], and on the P-cluster and FeMo-cofactor of nitrogenase [105, 107]. 

Hagen, W.R., Eady, R.R., Dunham, W.R., and Haaker, H. 1985b. A novel S = 3/2 EPR signal associated with native Fe-proteins of nitrogenase. FEBS Letters 189 250-254. 

Most common nitrogenase is composed of two proteins, Mo-Fe protein and Fe protein, both of which contain metal-sulfur clusters. The former protein... 

Most proteins contain more than one polypeptide chain. The manner in which these chains associate determines quaternary structure. Binding involves the same types of noncovalent forces mentioned for tertiary structure van der Waals forces, hydrophobic and hydrophilic attractions, and hydrogen bonding. However, the interactions are now interchain rather than infrachain (tertiary structure determination). The quaternary structure of hemoglobin (four almost identical subunits) will be discussed in Chapter 4, that of superoxide dismutase (two identical subunits) will be discussed in Chapter 5, and that of nitrogenase (multiple dissimilar subunits) will be discussed in Chapter 6. 

Table 3.1 Metal-Metal and Iron-Sulfur Bond Distances in Oxidized, Resting, and Reduced Forms of Nitrogenase s MoFe Protein...

Fe-protein interacts with MoFe-protein. Correct docking of Fe-protein to MoFe-protein is associated with conformational changes taking place during step 1. Steps 1 and 2 are prerequisites for all following nitrogenase reactions and for substrate reduction. 

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