The Mechanism of Action of Cobamide Coenzyme in the Ribonucleotide Reductase Reaction

摘要: When highly purified cobamide-dependent ribonucleotide reductase from Lactobacillus leichmannii is incubated with synthetically prepared 5, 6-dimethylbenzimidazolylcobamide 5'-deoxyadenosyl coenzyme containing tritium attached to carbon atom 5' of the deoxyadenosyl moiety (DBCC-5'-3H), transferred DBCC-5'-3H H2O in a reaction requiring substrate, enzyme, and dithiol reductant. At low enzyme concentrations, amount stoichiometrically equivalent reduced; hence, substrate-dependent release sensitive assay for reductase. unlabeled cobamide H2O-3H, as well 2'-deoxyribosyl product. The H2O-3H product decreases increasing concentration coenzyme. Coenzyme tritiated labels propionaldehyde dioldehydrase reaction. results indicate that functions an essential hydrogen-transferring agent reaction, hydrogen attaches moiety. We conclude although intermolecularly intramolecularly mechanism function same both reactions.