Ribonucleotide reductase and Pyruvate formate lyase
Ribonucleotide reductase (RNR) and pyruvate formate lyase (PFL) are believed to have diverged from a common ancestor. They have a structurally similar ten-stranded alpha-beta barrel domain that hosts the active site, and are radical enzymes. RNRs are found in all organisms and provide the only mechanism by which nucleotides are converted to deoxynucleotides. RNRs are separated into three classes based on their metallocofactor usage. Class I RNRs use a diiron-tyrosyl radical while Class II RNRs use coenzyme B12 (adenosylcobalamin, AdoCbl). Class III RNRs use an FeS cluster and S-adenosylmethionine to generate a glycyl radical. PFL, an essential enzyme in anaerobic bacteria, catalyzes the conversion of pyruvate and CoA to acteylCoA and formate in a mechanism that uses a glycyl radical.