Table 1. Enzymatic kinetics for the sucrose degradation by the isoforms of rice sucrose synthase.
| Sucrose+UDP | |||||
|---|---|---|---|---|---|
| Isoform | Phosphor-ylation | Km (mM) | Vmax (nmol min−1 (µg protein)−1) | kcat (min−1) | catalytic efficiency (min−1 mM−1) |
| Rsus1 | − | 219±50.6 | 3.23±0.25 | 295±33.7 | 1.33±0.15 |
| + | 160±49.0 | 3.37±0.21 | 308±14.7 | 1.80±0.26 | |
| Rsus2 | − | 82.7±26.5 | 2.73±0.06 | 255±5.13 | 3.80±1.32 |
| + | 74.7±8.62 | 3.83±0.47 | 355±44.5 | 4.77±0.67 | |
| Rsus3 | − | 525±54.2 | 1.63±0.06 | 149±8.39 | 0.29±0.01 |
| + | 384±93.0 | 1.67±0.20 | 151±18.0 | 0.41±0.06 | |
| Sucrose+ADP | |||||
| Isoform | Phosphor-ylation | Km (mM) | Vmax (nmol min−1 (µg protein)−1) | kcat (min−1) | catalytic efficiency (min−1 mM−1) |
| Rsus1 | − | 1799±358 | 1.47±0.15 | 129±14.2 | 0.08±0.01 |
| + | 1571±92.1 | 1.93±0.21 | 170±21.1 | 0.12±0.03 | |
| Rsus2 | − | 896±165 | 1.77±0.38 | 163±40.9 | 0.19±0.09 |
| + | 781±94.8 | 2.03±0.51 | 185±47.6 | 0.24±0.09 | |
| Rsus3 | − | 2085±89.6 | 1.40±0.17 | 128±19.2 | 0.06±0.01 |
| + | 1467±92.6 | 1.55±0.35 | 131±31.8 | 0.10±0.02 | |
Kinetic parameters, Km and Vmax, were evaluated by Lineweaver–Burk plots (Supplementary Figure 2), which were determined on the reactions for sucrose degradation (see Figure 2). Values were determined on the correlation between amounts of fructose generated and sucrose with UDP or ADP as substrates. kcat was estimated as Vmax/enzyme content. Catalytic efficiency was evaluated as the value of kcat/Km. Each value±SD is shown (n=5).