Table IV.
Specific activities and kinetic parameters of 20S proteasomes purified from T0, T24-starved, and T24 + Glc maize root tips
| Biochemical Parameters | T0 | T24 Starved | T24 + Glc |
|---|---|---|---|
| Specific activity (nmole mg−1 h−1) | |||
| Suc-L-L-V-Y-AMC | 104 ± 3 | 192 ± 0 | 124 ± 3 |
| Cbz-G-G-R-βNA | 204 ± 8 | 159 ± 15 | 185 ± 7 |
| Cbz-L-L-E-βNA | 54 ± 5 | 58 ± 9 | 42 ± 6 |
| 125I-Casein (μgcasein mg−1 h−1) | 381 ± 15 | 471 ± 25 | 388 ± 20 |
| Km (μm) | |||
| Suc-L-L-V-Y-AMC | 160 | 105 | 113 |
| Cbz-G-G-R-βNA | 274 | 397 | 199 |
| Cbz-L-L-E-βNA | 367 | 213 | 254 |
| kcat (s−1) | |||
| Suc-L-L-V-Y-AMC | 0.086 | 0.095 | 0.050 |
| Cbz-G-G-R-βNA | 0.085 | 0.100 | 0.040 |
| Cbz-L-L-E-βNA | 0.040 | 0.025 | 0.024 |
| kcat/Km (m−1 s−1) | |||
| Suc-L-L-V-Y-AMC | 537 | 905 | 442 |
| Cbz-G-G-R-βNA | 310 | 252 | 201 |
| Cbz-L-L-E-βNA | 109 | 117 | 94 |
Kinetic parameters were determined with the Lineweaver-Burk plot and linear fitting of four plots obtained from four different measurements. Ranges of substrates concentrations are: 10 to 200 μm for Suc-L-L-V-Y-AMC, and 20 to 170 μm for Cbz-G-G-R-βNA and Cbz-L-L-E-βNA.