Nitrogenase electron transfer pathways

Mr 220-250 kDa. Figure 1 shows an overall electron transfer pathway for the nitrogenases where the Fe proteins act as very specific, essential electron donors to the larger proteins. This is not the only role for the Fe proteins (see Section IV,C) and their role in the mechanism is almost certainly more complex than that of a simple electron transfer agent (see below. Section V). Electron transfer from the Fe protein to... 

The structure of FeMoCo (and the dinitrogen-binding protein) is unknown. The environment of the metals is constituted primarily of sulfur atoms, but the interpretation of the X-ray absorption fine structure (EXAFS) data on both the cofactor and protein (117-119) are contentious. It is not known whether the system in any specific part is aqueous or anhydrous, but oxygen destroys the activity. The electron-transfer pathway in the functioning nitrogenase is believed to be as shown in Scheme 22. 

Figure 12. The electron-transfer pathway for the action of the nitrogenases.

This involves a net transfer of eight electrons and the consumption of an unexpectedly large amount of ATP. This could hardly be a one-step reaction, and the questions regarding pathway and the existence of a nitrogenase complex remained. 

---