STRUCTURE AND REACTIVITY OF THE METAL CENTERS OF RIBONUCLEOTIDE REDUCTASES

The activation of the three classes of ribonucleotide reductases as fr ee radical enzymes is reviewed. Class I uses O-2 and a diferric mu-oxo center to generate a stable tyrosyl protein radical. Class II operate s with adenosyl cobalamin as the precursor of a putative transient thi yl protein radical. Class III forms an O-2-sensitive protein glycyl ra dical by the concerted action of an iron-sulfur cluster and (S)-adenos yl methionine.