Stopped-flow kinetic data have been obtained for a rapid electron-transfer reaction between the component proteins of nitrogenase from Klebsiella pneumoniae, which was induced by MgATP. Up to three equivalents of the Fe-containing protein were rapidly oxidized by one equivalent of the Fe-Mo-containing protein in a unimolecular reaction, k2 = 2 × 10(2)S-1. Evidence for a tight complex between the component proteins, KD(complex) less than 0.5 muM, which was formed with a rate k1 greater than 1 × 10(7)M-1-S-1, has been obtained. MgATP bound to either the Fe-containing protein or to the two-protein complex with a rate k3 greater than 2.5 × 10(6)M-1-S-1 and with KD(MgATP) = 0.4mM, before the electron-transfer reaction.

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