Ribonucleotide reductase iron content

All non-heme iron containing ribonucleotide reductases are also inhibited by hydroxyurea and related hydroxamates, while the adenosyl-cobalamin-dependent reductases are not affected (27, 156). The inhibition by these reagents can be partially reversed by excess Fe+2 or dithiols. Reaction of ribonucleotide reductase of E. coli with [14C]hydro-xyurea inactivated only the B2 subunit and this inactivation was not reversed by removal of the radioactivity (157). Inactivation by hydroxyurea does not affect the iron content of protein B2, but involves the destruction of the stable free radical (66,67). Reactivation can be accomplished by removal of the iron and reconstitution of apoprotein B2 with Fe+2. Hydroxyurea has been demonstrated to be a powerful radical scavenger in another system (158). 

Subunit B1 of . coli ribonucleotide reductase is an SH protein carrying several binding sites of different affinity for substrate and effector nucleotides these interactions will be discussed in a later paragraph. The most unusual features of the smaller subunit B 2 are its iron content and a tyrosine residue present as stable free radical. Both these components are essential for enzyme catalysis and structurally coupled. They confer characteristic light absorption to the protein, with a broad maximum around 370 nm (a =... 

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