On the Subunit Structure of Ribonucleoside Diphosphate Reductase

Proteins B1 and B2 of the ribonucleoside diphosphate reductase system of Escherichia coli B, which separately are enzymatically inactive, combine in the presence of Mg2+ to form a catalytically active complex demonstrable by sedimentation in sucrose gradients. Experiments employing gel filtration indicate that the B1 protein is capable of binding certain nucleoside triphosphates known to act as allosteric effectors on ribonucleotide reduction. These data indicate that the ribonucleoside diphosphate reductase of E. coli is composed of nonidentical protein subunits, of which one (B1) may serve a regulatory function through an ability to bind allosteric effectors.