. 2019 Nov 21;63(12):e01515-19. doi: 10.1128/AAC.01515-19

TABLE 2.

Kinetic parameters of purified β-lactamases CTX-M-33 and CTX-M-15

β-Lactam	CTX-M-33^a				CTX-M-15
β-Lactam	K_cat (s⁻¹)	K_m (μM)	K_cat/K_m (μM⁻¹ s⁻¹)	K_i (μM)	K_cat (s⁻¹)	K_m (μM)	K_cat/K_m (μM⁻¹ s⁻¹)	K_i (μM)
Penicillin G	210	20	10		28	100	0.3
Amoxicillin	215	160	1.35		15	90	0.15
Ticarcillin	7.5	40	0.2		3.5	30	0.1
Piperacillin	205	140	1.5		16	35	0.5
Cephalothin	380	30	12.5		50	45	1
Cefepime	70	100	0.7		20	480	0.03
Cefotaxime	620	215	3		60	30	2.2
Ceftazidime	0.35	1,500	0.0003		15	1,500	0.01
Imipenem	<0.01	ND	ND	0.2	<0.01	ND	ND	0.6
Meropenem	0.13	90	0.0014	0.0024	<0.01	ND	ND	0.017
Ertapenem	<0.01	ND	ND	0.009	<0.01	ND	ND	0.007
Aztreonam	10	60	0.2		7	85	0.08

Standard deviations were below 15%. ND, not determined due to a low initial rate of hydrolysis; k_cat, catalytic efficiency; K_m, Michaelis constant; k_cat/K_m, specificity constant; K_i, relative; k_off/k_on, ratio.