ABSTRACT
During the deamination of S-2-aminopropanol by the AdoCbl-dependent ethanolamine ammonia-lyase of Clostridia sp., a catalytic intermediate accumulates whose active site contains two paramagnetic species: cob(II)alamin and a free radical derived from the substrate molecule. Spin-echo spectroscopy has revealed that the unpaired electron on the substrate-derived radical is delocalized over a nitrogen atom that from its quadrupole splittings is probably a component of a secondary amide group. Experiments with 15N- and deuterium-labeled propanolamine gave no evidence of an interaction between this unpaired electron and the nitrogen originally attached to the substrate molecule. These results strongly suggest that the substrate-derived radical in this intermediate has already lost its nitrogen, and that this radical is stabilized by delocalization of the unpaired electron onto a nitrogen most likely situated in one of the peptide bonds of the enzyme backbone.
