The extents of formation of cobalt(II)-radical intermediates in the reactions with different substrates catalysed by the adenosylcobalamin-dependent enzyme ethanolamine ammonia-lyase.

1. The reactions of the adenosylcobalamin-dependent enzyme, ethanolamine ammonia-lyase, with the 'good' and 'relatively poor' substrates 2-aminoethanol and (S)-2-aminopropanol respectively, under conditions of saturation with substrate were investigated by rapid freezing in conjunction with electron paramagnetic resonance (e.p.r.) spectroscopy and by stopped-flow spectrophotometry. 2. In disagreement with earlier reports [Babior et al. (1972) J. Biol. Chem. 247, 4389-4392], it was found that the reaction of 2-aminoethanol gave an e.p.r. signal observed in rapid freezing experiments characteristic of a coupled Co(II)-free radical system. This signal was similar to, though not identical with, that obtained with (S)-2-aminopropanol. The steady-state level of the signal with 2-aminoethanol as substrate was 0.56 of that attained with (S)-2-aminopropanol. 3. The results of these e.p.r. experiments were shown to be consistent with stopped-flow data obtained under closely similar reaction conditions, the latter indicating a corresponding ratio of 0.64. The results also are consistent with those of a rapid wavelength scanning, stopped-flow spectrophotometric study [Hollaway et al. (1978) Eur. J. Biochem. 82, 143-154].