TABLE 3.
Catalytic constants for para-nitrophenyl-phosphate hydrolysis by StpA from parental strain D344S and ampicillin resistant mutants M1 and M2
| Substitution in StpA (strain) | Catalytic constants determined in the presence of Mn2+ ata: |
|||||
|---|---|---|---|---|---|---|
| 2 mM |
50 μM |
|||||
| Km (mM) | kcat (min−1) | kcat/Km (min−1 mM−1) | Km (mM) | kcat (min−1) | kcat/Km (min−1 mM−1) | |
| None (D344S) | 0.66 ± 0.09 | 1,200 ± 100 | 1,800 ± 300 | 0.69 ± 0.17 | 12 ± 1 | 17 ± 5 |
| T101R (M1) | 1.2 ± 0.2 | 0.83 ± 0.04 | 0.69 ± 0.12 | NDb | ND | ND |
| A35V (M2) | 1.0 ± 0.4 | 350 ± 40 | 350 ± 140 | 0.67 ± 0.28 | 0.22 ± 0.02 | 0.33 ± 0.14 |
a
Values ± SE of regression were obtained by fitting experimental data to the Michaelis-Menten equation, V = kcat ES/(Km + S), where V is the initial velocity and E and S are the initial enzyme and substrate concentrations, respectively.
b
ND, not determined.