Novel EPR signals associated with FeMoco centres of MoFe protein in MgADP-inhibited turnover of nitrogenase

Two novel electron paramagnetic resonance (EPR) signals arising from the [1 Mo-7Fe-9S-homocitrate] (FeMoco) centres of MoFe protein of Klebsiella pneum oniae nitrogenase (Kp1) were observed following turnover under M-ATP-limite d conditions. The combination of the nitrogenase Fe protein of Clostridium pasteurianum showed similar signals. The accumulation of MgADP under these conditions causes the normal EPR signal of dithionite-reduced Kp1 (with g = 4.3, 3.6, 2.01) to be slowly converted to novel signals with g = 4.74, 3.3 2, 2.00 and g = 4.58, 3.50, 1.99. These signals do not form in incubation o f protein mixtures containing only MgADP, thus they may be associated with trapped intermediates of the catalytic cycle. (C) 2001 Federation of Europe an Biochemical Societies. Published by Elsevier Science B.V. All rights res erved.