Abstract
During turnover at 10 degrees C at pH 7.4 in the presence of ethylene, the MoFe protein of Klebsiella pneumoniae nitrogenase (Kp 1) exhibited an electron-paramagnetic-resonance signal with g-values at 2.12, 1.998 and 1.987. 57Fe isotopic substitution demonstrated that this signal arose from the Kp 1 FeMo-cofactor in an S = 1/2 spin state.