Ethanolamine ammonia-lyase has a "base-on" binding mode for coenzyme B-12

Ethanolamine ammonia-lyase (EAL, EC 4.3.1.7) catalyzes a coenzyme B-12-depe ndent deamination of vicinal amino alcohols, The mode of binding of coenzym e B-12 to EAL has been investigated by electron paramagnetic resonance spec troscopy (EPR) using [N-15]-dimethylbenzimidazole-coenzyme B-12. EAL was in cubated with either unlabeled or N-15-enriched coenzyme B-12 and then eithe r exposed to light or treated with ethanol to generate the cleaved form of the cofactor, cob(II)alamin (B-12r) bound in the active site. The reaction mixtures were examined by EPR spectroscopy at 77 K, N-15 superhyperfine spl itting in the EPR signals of the low-spin Co2+ of B-12r, bound in the activ e site of EAL, indicates that the dimethylbenzimidazole moiety of the cofac tor contributes the lower axial ligand consistent with "base-on" binding of coenzyme B-12 to EAL, (C) 1999 Academic Press.