Nitrogenase MoFe protein sources

The two nitrogenase proteins, Fe-protein and MoFe-protein, are composed of a total of three different types of subunits and contain three different types of metal centers. The properties of the nitrogenase proteins have been extensively studied and are summarized below. To distinguish the two nitrogenase proteins isolated from different bacterial sources, the MoFe-protein and Fe-protein are designated as components 1 and 2, respectively, preceded by a two-letter abbreviation of the source species and genus i.e., Avl is MoFe-protein isolated from Azotobacter vinelandii and Cp2 is Fe-protein isolated from Clostridium pasteurianum, etc. 

The evidence in the foregoing sections indicates that the Fe protein accepts electrons from the electron donor and that the MoFe protein binds the reducible substrate. Evidence from several sources and techniques, principally epr and Mossbauer spectroscopy and stopped-flow spectrophotometry, shows that electrons pass from the Fe protein to the MoFe protein with the concomitant hydrolysis of ATP. The earliest evidence came from steady-state epr studies on the nitrogenase of K. pneumoniae (Smith et al., 1972), A. vinelandii and C. pasteurianum (Orme-Johnson et al., 1972 Palmer et al., 1972 Zumft et al., 1972). In the presence of sodium dithionite and without MgATP, the epr spectra of the two proteins are additive. When ATP is added both spectra are largely bleached within (it is now agreed) the turnover time (185 ms/electron pair at 23 C) of the enzyme and remain so imtil the dithio-... 

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