Table 1.
Kinetic parameters characterizing the cleavage of poly(I) and GpU by RNase Sa and six mutants at 25°C and pH 6.5
| RNase | Substrate | kcat (sec−1) | KM × 104 (M) | kcat/KM × 10−4 (M−1 sec−1) |
| Wild type | poly(I) | 178 ± 10 | 1.51 ± 0.15 | 117.9 |
| GpU | 1.9 ± 0.1 | 5.5 ± 0.3 | 0.35 | |
| Gln38Ala | poly(I) | 23 ± 2 | 2.5 ± 0.2 | 9.2 |
| Glu41Lys | poly(I) | 173 ± 11 | 1.6 ± 0.2 | 108 |
| GpU | 1.8 ± 0.1 | 10.0 ± 0.5 | 0.18 | |
| Glu54Gln | poly(I) | 0.50 ± 0.05 | 3.1 ± 0.3 | 0.16 |
| Arg65Ala | poly(I) | 0.21 ± 0.03 | 2.0 ± 0.2 | 0.11 |
| Glu74Lys | poly(I) | 34 ± 4 | 1.7 ± 0.2 | 20 |
| GpU | 0.50 ± 0.05 | 5.7 ± 0.3 | 0.09 | |
| His85Glna | poly(I) | — | — | <0.007 |
a No activity was observed at enzyme concentrations below 1 • 10−6 M.