Table 3.
Comparison of the kinetic parameters of acetylthiocholine hydrolysis and effects of the specific inhibitors of AChE (IC50) on the free AChE and that associated with amyloid-β fibrils
| Parameter | AChE | AChE–Aβ complex |
|---|---|---|
| Kinetic parameters | ||
| Km(mm) | 0.097 ± 0.007 | 0.764 ± 0.025* |
| Vmax (μmol/min/ml) | 0.129 ± 0.015 | 0.222 ± 0.029* |
| Kss(mm) | 30.4 ± 1.1 | 48.1 ± 8.5** |
| Optimal pH | 7.5–8.0 | 7.0 |
| Activity at pH 5.0 (%) | 3.2 ± 0.8 | 41.1 ± 3.0* |
| IC50 values | ||
| Tacrine (nm) | 445.0 ± 17.6 | 1074.8 ± 73.3* |
| Edrophonium (μm) | 5.36 ± 0.48 | 17.6 ± 4.6*** |
| Propidium (μm) | 34.6 ± 1.20 | 72.0 ± 4.8* |
| Inhibition coefficients (Ki) | ||
| Tacrine (nm) | 51.0 | 542.4 |
| Edrophonium (μm) | 0.61 | 8.90 |
| Propidium (μm) | 3.96 | 36.3 |
The Km and Vmax was determined from Lineweaver–Burk plots (1/V vs 1/S), with 0.03–1.0 mm acetylthiocholine.Kss was determined by plotting of 1/Vas a function of substrate concentration (0.1–50 mm). For determination of IC50 values, samples were incubated with appropriate concentrations of the various inhibitors for 30 min at room temperature, and the AChE activity was determined colorimetrically.Ki values are determined as specified in Materials and Methods. Values represent means ± SD of four to six separate assays made in duplicate for AChE and three to five for AChE–Aβ complex.
*Significantly different from control with p < 0.001 by nonparied Student’s t test; ***p < 0.01; **p < 0.05.