Phosphines are ribonucleotide reductase reductants that act via C-terminal cysteines similar to thioredoxins and glutaredoxins.

Ribonucleotide reductases (RNRs) catalyze the formation of 2'-deoxyribonucleotides. Each polypeptide of the large subunit of eukaryotic RNRs contains two redox-active cysteine pairs, one in the active site and the other at the C-terminus. In each catalytic cycle, the active-site disulfide is reduced by the C-terminal cysteine pair, which in turn is reduced by thioredoxins or glutaredoxins.

Ribosylurea accumulates in yeast urc4 mutants.

Yeast Saccharomyces (Lachancea) kluyveri urc4 mutants, unable to grow on uracil, biotransformed (14)C(2)-uracil into two labeled compounds, as detected by high performance liquid chromatography (HPLC). These two compounds could also be obtained following organic synthesis of ribosylurea. This finding demonstrates that in the URC pyrimidine degradation pathway, the opening of the uracil ring takes place when uracil is attached to the ribose moiety.

Metal binding and activity of ribonucleotide reductase protein R2 mutants: conditions for formation of the mixed manganese-iron cofactor.

Class Ic ribonucleotide reductase (RNR) from Chlamydia trachomatis (C. tm.) lacks the tyrosyl radical and uses a Mn(IV)-Fe(III) cluster for cysteinyl radical initiation in the large subunit.

Chlamydial ribonucleotide reductase: tyrosyl radical function in catalysis replaced by the FeIII-FeIV cluster.

Ribonucleotide reductase (RNR) from Chlamydia trachomatis is a class I RNR composed of proteins R1 and R2. In protein R2, the tyrosine residue harboring the radical that is necessary for catalysis in other class I RNRs is replaced by a phenylalanine. Active C.