Comparison of apparent affinity for substrates of potato tuber wild-type and mutant ADPGlc PPases
| ADPGlc PPase | Synthesis Direction | Pyrophosphorolysis Direction | ||
|---|---|---|---|---|
| S0.5 for Glc-1-P | Vmax | S0.5for ADPGlc | Vmax | |
| mm | units mg−1 | mm | units mg−1 | |
| Wild type | 0.057 ± 0.003 (1.1) | 48 ± 1 | 0.20 ± 0.01 (1.3) | 55 ± 1 |
| SK198RLwt | 7.7 ± 0.1 (1.3) | 24 ± 1 | 0.49 ± 0.02 (1.1) | 16 ± 1 |
| SK198ALwt | 22.0 ± 2.5 (1.5) | 46 ± 3 | 1.3 ± 0.1 (1.0) | 20 ± 1 |
| SK198ELwt | 31.1 ± 2.7 (1.8) | 1.7 ± 0.1 | 2.1 ± 0.2 (1.0) | 1.4 ± 0.1 |
| SwtLK213R | 0.044 ± 0.002 (1.1) | 27 ± 1 | 0.36 ± 0.03 (1.8) | 37 ± 1 |
| SwtLK213A | 0.037 ± 0.001 (1.0) | 25 ± 1 | 0.46 ± 0.02 (1.7) | 31 ± 1 |
| SwtLK213E | 0.036 ± 0.001 (0.9) | 31 ± 1 | 0.68 ± 0.01 (1.8) | 45 ± 1 |
| SK198RLK213R | 5.6 ± 0.1 (1.5) | 24 ± 1 | 0.72 ± 0.01 (1.9) | 14 ± 1 |
Reactions were performed in either the synthesis (assay II) or the pyrophosphorolysis direction (assay I) as described in Methods. Data represent the average of two identical experiments ± the average difference of the duplicates. The values in parentheses are the Hill interaction coefficients (n H). One unit of enzyme activity is expressed as the amount of enzyme required to form 1 mol of ADPGlc per minute at 37°C assayed in either the synthesis or the pyrophosphorolysis direction.