Table 1.

Attributes of RNase 1-PEG Conjugates In Vitro.

Ribonuclease	kcat/KM (107 M-1 s-1)*	Kd (nM)†	IC50 (µM)†
Wild-type RNase 1	2.9 ± 0.1	2.9 x 10-7	>25
5-kDa mPEG.G89C RNase 1	2.6 ± 0.3	<1.4	>50
20-kDa mPEG.G89C RNase 1	6.8 ± 0.1	<1.4	>50
60-kDa mPEG2.G89C RNase 1	6.1 ± 0.3	<1.4	>50
ONC	0.0018 ± 0.00005	150 ± 50	0.22 ± 0.01

^*Values of k_cat/K_M (±SE) are for the catalysis of 6-FAM-dArU(dA)₂-6-TAMRA cleavage at room temperature in 0.10 M MES-NaOH buffer (pH 6.0) containing NaCl (0.10 M). The values for RNase 1 and ONC were reported previously [11].

^†Values of K_d (±SE) are for the complex with human RI at room temperature. The values for wild-type RNase 1 [8] and ONC [37] were reported previously.

^‡Values of IC₅₀ (±SE) are for the incorporation of [methyl-³H]thymidine into the DNA of K-562 cells. Data are from Figure 3.