Ribonucleotide Reductase

Ribonucleotide reductase catalyzes the essential step in the formation of all four deoxynucleotides. Although the earliest form of the enzyme emerged in a reducing environment, additional forms evolved to function in an aerobic state. While the different classes of this enzyme have different cofactors, and different mechanisms for generating the free radical necessary for the reaction, they have retained many of the key regulatory features. Most of the microbial enzymes have one regulatory site, while the enzyme from E. coli and most eukaryotes normally has two. Regulation at these sites by nucleotide effectors permits the enzyme to alter its selection for any of the four ribonucleotide substrates.