Ethanolamine ammonia-lyase: inactivation of the holoenzyme by N2O and the mechanism of action of Coenzyme B12.

Functional ethanolamine ammonia-lyase is inactivated by N2O as well as by O2, indicating that the active form of coenzyme B12 is an enzyme-bound corrin derivative in which the Co-C bond of the coenzyme is broken and the cobalt ion is in the +1 state of oxidation. The nucleoside fragment formed in the process of coenzyme activation is tentatively identified as 4',5'-didehydro-5'-deoxyadenosine. A mechanism of action of ethanolamine ammonia-lyase is formulated in analogy to that of DL-1,2-Propanediol dehydrase and compared to proposed alternative reaction schemes.