Table 1. Proteolytic activity data for IDE in the presence of α-synuclein.
| Syn (μM) | kcat (s−1) | KM(μM) | n | kcat/KM(M−1s−1) | |
|---|---|---|---|---|---|
| 1 μM IDE | 0 | 0.020 ± 0.001 | 20.1 ± 2.4 | 1.3 ± 0.1 | 1010 |
| 1 | 0.024 ± 0.001 | 22.5 ± 1.6 | 1.4 ± 0.1 | 1070 | |
| 10 | 0.025 ± 0.002 | 21.6 ± 2.3 | 1.5 ± 0.2 | 1170 | |
| 100 | 0.058 ± 0.009 | 49.0 ± 13.2 | 1.2 ± 0.1 | 1190 | |
| Syn (μM) | kcat (s−1) | KM (μM) | n | kcat/KM | |
| 3 μM IDE | 0 | 0.241 ± 0.005 | 9.5 ± 0.4 | 1.9 ± 0.1 | 25400 |
| 3 | 0.308 ± 0.010 | 11.2 ± 0.8 | 1.8 ± 0.2 | 27560 | |
| 35 | 0.397 ± 0.026 | 13.0 ± 1.6 | 1.6 ± 0.2 | 30490 | |
| 70 | 0.286 ± 0.009 | 10.0 ± 0.7 | 1.9 ± 0.2 | 28700 | |
| Amylin (μM) | kcat (s−1) | KM (μM) | n | kcat/KM | |
| 1.6 μM IDE | 0 | 0.082 ± 0.004 | 26 ± 2 | 1.3 ± 0.1 | 3100 |
| 10 | 0.057 ± 0.006 | 41 ± 7 | 1.3 ± 0.1 | 1400 |
Enzymatic parameters (kcat, KM, n, kcat/KM) for IDE proteolytic activity on substrate V as a function of α-synuclein concentrations for two different IDE concentrations (1 and 3 μM) (data shown in Fig. 3). The initial rate versus substrate concentration data was fitted to an equation for a sigmoidal curve providing best fit values for kcat, KM, and n. kcat is often referred to as the turn-over number and denotes the maximum number of enzymatic reactions catalyzed per second; KM is an apparent dissociation constant that reflects the enzyme concentration where the rate of the enzyme reaction is half maximal; and finally, n reports on the cooperativity of the reaction with n = 1 lacking cooperativity. The ratio kcat/KM corresponds to a pseudo-second order rate constant and reports on the catalytic efficiency. The variations in enzymatic parameters for 1 and 3 μM IDE as a function of α-synuclein are graphically visualized in Figure S7.