Electron Tansport to Nitrogenase in Klebsiella pneumoniae. Purification and Properties of the nifj Protein

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Abstract
In K. pneumoniae, the physiological electron flow to nitrogenase (EC 1.18.2.1) involves specifically, in addition to nitrogenase reductase, the products of the nifF and nifJ genes. The J protein was purified to homogeneity and was found to be an Fe-S protein devoid of Mol. In its native state, the J protein is a dimer of MW .apprx. 245,000, made up of 2 subunits of the same MW. It contains .apprx. 30 mol Fe and 24 mol labile S/mol protein. The addition of J protein to crude extracts of a nifJ mutant reestablishes pyruvate-supported acetylene-reducing activity. This activity is further enhanced by the addition of pure nitrogenase (Kp1). Based on its physical properties, the J protein is probably an oxidoreductase with a possible physiological role of transferring electrons from a metabolic donor to the F protein. Another protein with activity that is dependent on the nifJ gene also seems to be required for the formation of a fully active Kp1.