Table 2. Characteristics of the Ribonucleotide Reductase Small Subunits Proteins.

Ribonucleotide Reductase activity was presented as formation of dCDP (see Materials and Methods), and was measured in the presence of 0.059 μM (5 μg) of R1 protein and 0.057 μM (2.5 μg) of hRRM2 or hp53R2 proteins with a total sample volume of 100 μl. Each value is the average of two to three determinations with deviations < 0.3. ND: not detectable. Iron quantification is performed on freshly purified protein using atomic absorption spectrometry with lower limit > 0.01. The radical content was quantified against a standard solution of 1mmol/L CuSO4 in 50mmol/L EDTA by double integration of spectra registered at no saturating microwave levels using standard Bruker method. The lowest limit of detection is 0.001.

Proteins	Specific Activity (nmol/min/mg R2)	Iron Content (mol/mol R2, %)	Radical Content (mol/mol R2)
hp5 3R2
wild type	4152 ± 96	1.53 ± 0.26 100	0.82
F183Y	4592 ± 176	1.82 ± 0.27 119	0.90
Y124W	1352 ± 104	0.84 ± 0.10 55	0.27
Y124W/F183Y	192 ± 24	0.56 ± 0.07 37	0.04
Q127V	384 ± 88	0.40 ± 0.16 26	0.08
Q127K	ND	0.24 ± 0.11 16	ND
Q127E	376 ± 24	0.68 ± 0.12 44	0.07
Q127N	160 ± 48	0.80 ± 0.02 52	0.03
hRRM2
wild type	6000 ± 96	3.10 ± 0.58 100	1.23
Y221F	4456 ± 248	1.45 ± 0.42 47	0.91
Y162W	208 ± 16	0.72 ± 0.13 23	0.04
Y162W/Y221F	1304 ± 152	0.95 ± 0.07 31	0.27
Q165V	232 ± 48	0.62 ± 0.14 20	0.05
Q165K	ND	0.34 ± 0.04 11	ND
Q165E	480 ± 136	0.70 ± 0.12 22	0.10
Q165N	400 ± 24	0.50 ± 0.06 16	0.08