TABLE 4.

Kinetic parameters of several β-lactam antibiotics for the purified AmpC β-lactamase (ACC-2) of H. alvei 1 from a culture of E. coli DH10B(pDEL-1)^a

Substrate	kcat (s−1)	Km (μM)	kcat/Km (nM−1 s−1)
Benzylpenicillin	8.1	10	816
Amoxicillin	0.2	<1	>0.2
Ticarcillin	<0.05	—	—
Piperacillin	7.7	14	550
Cephalothin	300	13	23,100
Cefoxitin	<0.01	—	—
Ceftazidime	0.03	5.2	7
Cefotaxime	0.02	19	1
Cefepime	3.6	147	24
Cefpirome	1.2	5.2	240
Imipenem	<0.01	—	—
Aztreonam	<0.05	—	—

^aValues are means of three independent measures. —, not determinable (the initial rate of hydrolysis was lower than 1 nM⁻¹ s⁻¹).