TABLE 1 .
Catalytic constants for pNPP hydrolysis by StpA from parental strain D344S and ampicillin-resistant mutants
| Substitution in StpA (strain) | Catalytic constanta in presence of Mn2+ at: |
|||||
|---|---|---|---|---|---|---|
| 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 ± 290 | 0.69 ± 0.17 | 12 ± 1 | 17 ± 4.5 |
| T101R (M1) | 1.2 ± 0.2 | 0.83 ± 0.04 | 0.69 ± 0.12 | NDb | ND | ND |
| D136Y (Mb) | 1.8 ± 0.5 | 140 ± 15 | 80 ± 23 | 1.5 ± 0.4 | 0.09 ± 0.01 | 0.06 ± 0.02 |
| D18Y (Md) | ND | ND | <0.003 | ND | ND | ND |
| S120R (Me) | 1.3 ± 0.1 | 28 ± 0.1 | 22 ± 1.6 | 2.6 ± 0.7 | 0.23 ± 0.02 | 0.09 ± 03 |
a
Regression values ± standard errors 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.