Table II.

Kinetic parameters of the potato tuber wild-type and mutant ADPGlc PPases

ADPGlc PPaseSynthesis DirectionI0.5 for PiPyrophosphorolysis Direction
S0.5A0.5for 3PGAS0.5 for PPi
for ATPfor Mg2+
μm mm mm μm
Wild type76  ± 2 (1.6)2.2  ± 0.1 (3.7)0.14  ± 0.01 (0.9)1.4  ± 0.1 (1.4)41  ± 3 (1.0)
SK198RLwt 119  ± 1 (1.5)3.7  ± 0.1 (2.1)0.39  ± 0.04 (1.3)2.8  ± 0.2 (1.3)210  ± 10 (1.5)
SK198ALwt 130  ± 4 (1.3)2.8  ± 0.1 (2.5)0.15  ± 0.01 (1.2)5.0  ± 0.1 (1.1)135  ± 5 (1.5)
SK198ELwt 102  ± 24 (1.4)2.6  ± 0.1 (1.7)0.07  ± 0.01 (1.3)10.0  ± 0.2 (1.2)240  ± 10 (1.6)
SwtLK213R 125  ± 6 (1.5)2.0  ± 0.1 (3.6)0.37  ± 0.01 (0.8)0.7  ± 0.1 (1.0)43  ± 2 (0.8)
SwtLK213A 129  ± 1 (1.4)2.1  ± 0.1 (3.4)0.32  ± 0.03 (1.0)0.9  ± 0.1 (1.3)28  ± 2 (1.5)
SwtLK213E 170  ± 8 (1.4)1.9  ± 0.1 (3.9)0.36  ± 0.02 (0.9)0.7  ± 0.1 (1.2)33  ± 1 (1.3)
SK198RLK213R 320  ± 20 (1.7)3.5  ± 0.2 (1.8)1.6  ± 0.1 (1.6)1.3  ± 0.1 (1.2)230  ± 10 (1.2)

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). The 3PGA concentration used was 3 mm for the wild-type enzyme and the single-mutant enzymes, and 3PGA at 10 mm was used for the double-mutant enzyme.