THE FUNCTION OF ADENOSYLCOBALAMIN IN THE MECHANISM OF RIBONUCLEOSIDE TRIPHOSPHATE REDUCTASE FROM LACTOBACILLUS-LEICHMANNII

Ribonucleoside triphosphate reductase from Lactobacillus leichmannii c atalyzes the reduction of nucleotides to deoxynucleotides and uses ade nosylcobalamin as a cofactor. A transient protein-based thiyl radical is essential for catalysis. Studies directed toward the elucidation of the function of adenosylcobalamin during catalysis have shown that fo rmation of the thiyl radical and 5'-deoxyadenosine occurs in a concert ed fashion with C-Co bond homolysis, that the homolysis is entropicall y and not enthalpically driven, that the dimethylbenzimidazole moiety of adenosylcobalamin is the axial ligand during catalysis, and that th e C-Co bond is reformed after every turnover.