Three Different Ribonucleotide Reductase Classes

The common denominators of RNRs are radical chemistry involving redox active cysteines (see sections 3.1 and 3.3) and with few exceptions an allosteric control mediated by deoxyribonucleoside triphosphates (dNTPs) and ATP (Reichard, 1997). Yet, several other characteristics distinguish the three RNR classes (Table 1) from each other  

Type of class Polypeptide composition Gene nomenclature Stable radical/ cofactor Metal site/ cofactor Substrate Reductant (s )  

I 2P2 nrdA/nrdE nrdB/nrdF lyr. Diiron-oxo NDP Thioredoxin Glutaredoxin NrdH-redoxin 4-11 

III 2(P2) nrdD nrdG Gly Iron-sulphur AdoMef NTP Formate 3 

The tyrosyl radical and the diiron-oxo centre is confined to the (or NrdB/NrdF) component. 

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Ribonucleotide reductases (RNR) from different origins have been shown to contain different metal ions and require different cofactors. This has led to a systematic definition of three major classes at present,... 

Introduction Three Classes of Ribonucleotide Reductases with Different Metal Cofactors cind Free Radicals... 

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