Table 2.

Kinetic parameters (± SD) for the initial ( Vo) and steady-state ( Vss) phases of hydrolysis of β-lactams by OXA-10 and -16 β-lactamase in 0.1 M phosphate buffer (pH 7.0) at 37°C

SubstrateOXA-10
VssVoInitial β-lactamase concnb(μM)
Km(μM)kcat(s−1)kcat/ KmaKm(μM)kcat(s−1)Kcat/Km
Penicillin G 63 ± 6 c 89 ± 10 1,410  -e --0.61
Ampicillin 235 ± 30 5,590 ± 30 2,500 77 ± 9 531 ± 12 6,900 0.3
Carbenicillin 195 ± 13 31 ± 1 159 370 ± 44 126 ± 5 340 0.61
Oxacillin 222 ± 16 608 ± 10 2,740 96 ± 8 660 ± 10 6,870 0.61
Cloxacillin 2,640 ± 323 530 ± 36 196 1,110 ± 100 2,680 ± 150 2,420 1.21
Cephaloridine 2,340 ± 300 79 ± 8 33 395 ± 83 39 ± 3 98 0.61
Cephalothin38 ± 26 ± 0.1158---3.03
Cefotaxime346 ± 199 ± 0.226---2.43
Ceftriaxone55 ± 23 ± 0.354---12.13
CeftazidimeNDd NDND---12.13
OXA-16
VxxVoInitial β-lactamase concnb (μM)
Km (μM)kcat(s−1)kcat/ KmaKm(μM)kcat(s−1)kcat/Km a
65 ± 1 48 ± 1 738 <20 >60 -1.74
205 ± 21 97 ± 4 473 142 ± 31 163 ± 8 1,150 0.58
129 ± 32 17 ± 1 132 150 ± 26 69 ± 4 460 0.82
960 ± 159 411 ± 36 428 660 ± 120 455 ± 35 758 0.44
2,080 ± 333 264 ± 25 127 1,120 ± 261 1,200 ± 137 1,070 0.82
424 ± 40 21 ± 1 50 379 ± 61 30 ± 2 79 0.82
32 ± 33 ± 194---1.74
346 ± 43 6 ± 0.5 17 157 ± 40 10 ± 0.5 64 0.82
36 ± 21.4 ± 0.539---1.74
NDNDNDNDNDND1.74
  • a ( kcat/ Km) × 1,000, in micromolar−1 second−1.

  • b Concentration of the stock enzyme from which samples were taken to start the assays before dilution with substrate.

  • c Cases where Vo and Vss were significant are indicated in boldface.

  • d ND, hydrolysis not detected.

  • e -, linear kinetics, so Vo corresponds to Vss.