Ribonucleotide reductases: radical enzymes with suicidal tendencies.

Ribonucleotide reductases isolated from E. coli and from L. leichmannii differ considerably in their primary and quaternary structures, as well as in their cofactor requirements. Despite these differences, studies with the wt enzymes and the normal substrate, and with the wt enzymes and a variety of mechanism-based inhibitors, demonstrate amazing mechanistic similarities between the two reductases. Recent studies with five cysteine mutants of both reductases reveal strikingly similar phenotypes, indicating that, despite the differences in the primary structures, the groups involved in catalysis in both enzymes appear to be similar.