TABLE 2.

Kinetic parameters for the purified β-lactamases TUS-1 and MUS-1a

SubstrateTUS-1MUS-1
kcat (s−1)cKm (μM)bkcat/Km (mM−1 · s−1)ckcat (s−1)cKm (μM)bkcat/Km (mM−1 · s−1)c
Benzylpenicillin320784,000170404,200
Amoxicillin4904801,000400560700
Ticarcillin1151637003441502,200
Piperacillin9907513,5003301602,020
Cephaloridine1260020100580170
Cephalothin401253009097900
Cefuroxime30241,2001515870
Cefoxitin178202071,3005
Moxalactam>90>2,000ND>70>2,000ND
Cefotaxime80105470125180700
Ceftazidime1514701031,7132
Cefepime>1>2,000ND>1>2,000ND
Cefpirome>6>2,000ND>1>2,000ND
AztreonamNDNDNDND
Imipenem225250900240470500
Meropenem1701,0601602501,400180
  • a Values are expressed as the means of three independent measures (standard deviations were within 15%).

  • b —, not hydrolyzed (i.e., the initial rate of hydrolysis was lower than 0.01 μM−1·s−1).

  • c ND, not determinable due to too-high Km value.