TABLE 1.
Kinetic parameters for interactions of nitrocefin and PBP 2a at pH 5.0 and 7.0
The parameters apply to the minimal kinetic scheme E + N ⇄ EN → E-N → E + P, where E is the PBP 2a, N is nitrocefin, EN is the noncovalent complex between PBP 2a and nitrocefin, E-N is the covalent complex between PBP 2a and nitrocefin (acyl-enzyme), and P is the product of hydrolysis of nitrocefin. The ⇄ arrows refer to the reversible formation of the non-covalent complex EN (with dissociation constant Kd), the first → arrow refers to the formation of the acylated enzyme (with rate constant k2), and the second → arrow refers to the deacylation reaction (with rate constant k3). k2/Kd is the second order rate constant for the bimolecular encounter between nitrocefin and PBP 2a.
|
Parameter
|
pH
|
|
|---|---|---|
| 7.0 | 5.5 | |
| Kd (μm) | 195 ± 28 | 100 ± 30 |
| k2 (s-1 × 103) | 6.0 ± 0.6 | 15.2 ± 1.5 |
| k3 (s-1 × 106) | 2.5 ± 0.2 | 2.8 ± 0.2 |
| k2/Kd (s-1m-1) | 31 ± 3 | 150 ± 14 |