TABLE 4.

Michaelis constants

Antibiotic and enzymeKm (μM)kcat (s−1)kcat/Km (10−6 M−1 s−1)
Benzylpenicillin
    SHV-128 ± 6980 ± 4535 ± 6
    Gly238Ser13 ± 532 ± 22.5 ± 0.8
    Gly238Ala3.40 ± 0.0337.0 ± 0.111 ± 0.1
Ampicillin
    SHV-1120 ± 272,400 ± 21420 ± 2.7
    Gly238Ser10 ± 230 ± 23.0 ± 0.4
    Gly238Ala31.0 ± 4.4180 ± 145.8 ± 0.37
Cephaloridine
    SHV-150 ± 10150 ± 133 ± 0.34
    Gly238Ser40 ± 13500 ± 14410 ± 0.2
    Gly238Ala16 ± 336.0 ± 0.22.3 ± 0.4
Nitrocefin
    SHV-15.0 ± 0.9142 ± 428.4 ± 4
    Gly238Ser10 ± 237 ± 24 ± 0.5
    Gly238Ala3.2 ± 0.346 ± 114 ± 0.3
Cefotaxime
    SHV-1NMaNM
    Gly238Ser9 ± 26.0 ± 0.40.6 ± 0.1
    Gly238Ala12.4 ± 0.84.40 ± 0.010.4 ± 0.02
  • a NM, not measurable.