Flavodoxins are low-potential electron donors to a number of redox enzymes. NifF is the electron donor to nitrogenase, and is thus implicated in nitrogen fixation. Does not function as an electron donor to nitrite reductase. E(0) is -493 mV. It is the mid-point potential of the semiquinone/hydroquinone redox couple (SQ/HQ) of AvFld 2. Is the predominant flavodoxin expressed when A.vinelandii is grown on N(2) as nitrogen source. Is also synthesized during growth on nitrate, but in less abundance than AvFld 1. Belongs to the flavodoxin family.