TABLE 3.
Enzyme |
kcat (s−1)
|
Km (μM)
|
kcat/Km (μM−1 s−1)
|
Relative kcat/km
|
||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
AMP | IMP | CTX | AMP | IMP | CTX | AMP | IMP | CTX | AMP | IMP | CTX | |
SME-1 | 58 ± 4 | 185 ± 5 | NDa | 590 ± 17 | 535 ± 27 | ND | 0.10 | 0.35 | 0.0064b | 1 | 1 | 1 |
SME H105R | 5.7 ± 0.8 | 1.1 ± 0.3 | ND | 185 ± 45 | 159 ± 52 | ND | 0.031 | 0.007 | 0.014b | 0.3 | 0.02 | 2.2 |
SME H105W | 45 ± 2 | 230 ± 7 | ND | 132 ± 17 | 442 ± 23 | ND | 0.34 | 0.52 | 0.0093b | 3.4 | 1.5 | 1.5 |
SME H105Y | 25 ± 9 | 566 ± 54 | ND | 150 ± 113 | 1801 ± 165 | ND | 0.17 | 0.31 | 0.0038b | 1.7 | 0.9 | 0.6 |
kcat and Km not determined (ND) directly because it is assumed that Km ≫ [S].
kcat/Km determined using v0 = kcat/Km [E][So], where vo is velocity, E is enzyme concentration, S0 is initial substrate concentration.
AMP, ampicillin; IMP, imipenem; CTX, cefotaxime.