Table 1.
Effect of salts and urea on LF activity.
| Relative ionic strength | IC50 (mM) | Ionic strength at IC50 (mM)a | |
|---|---|---|---|
| GdnHCl | 1 | 140 (±10) | 165 |
| GdnSCN | 1 | 140 (±12) | 165 |
| (Gdn)2SO4 | 3 | 50 (±5) | 175 |
| NaCl | 1 | 150 (±15) | 175 |
| NaSCN | 1 | 150 (±10) | 175 |
| Na2SO4 | 3 | 50 (±7) | 175 |
| MgSO4 | 4 | 25 (±4) | 125 |
| Urea | 0 | 1050 (±100) | 25 |
LF (50 nM) in Hepes buffer (50 mM, pH 7.4) was incubated in the presence of salts or urea for 30 min prior to the initiation of the assay by addition of S-pNA (10 μM). IC50 values represent the mean (±1 s.d.) of three independent experiments.
a
The ionic strength of 50 mM Hepes at pH 7.4 (i.e., 25 mM) was taken into account in the calculation of the ionic strength at the IC50 value.