TABLE 3.

Kinetic parameters of GES-4, GES-3, and GES-2

Substrate	GES-4			GES-3			GES-2c
	Km (μM)	kcat (s−1)	kcat/Km (M−1 s−1)	Km (μM)	kcat (s−1)	kcat/Km (M−1 s−1)	Km (μM)	kcat (s−1)	kcat/Km (M−1 s−1)
Benzylpenicillin	160 ± 10	130 ± 10	7.8 × 105	33 ± 7	15 ± 1	4.5 × 105	4	0.4	9.6 × 104
Ampicillin	62 ± 4	19 ± 11	3.1 × 105	120 ± 30	23 ± 4	1.9 × 105	NPe	NP	NP
Cephaloridine	2,200 ± 400	490 ± 30	2.3 × 105	2,300 ± 100	270 ± 10	1.2 × 105	7.7	0.5	6.5 × 104
Cefotaxime	700 ± 200	17 ± 6	2.4 × 104	1,100 ± 100	120 ± 10	1.1 × 105	890	2.2	2.5 × 103
Ceftazidime	1,500 ± 400	2.5 ± 0.5	1.7 × 103	990 ± 130	23 ± 2	2.3 × 104	>3,000	NDd	ND
Cefpirome	340 ± 70	3.6 ± 0.4	1.1 × 104	550 ± 30	36 ± 2	6.6 × 104	NP	NP	NP
Cefoxitin	810 ± 70	85 ± 3	1.1 × 105	NH	NC	NC	—f	—	—
Cefminox	370 ± 70	7.7 ± 2.0	2.0 × 104	NH	NC	NC	NP	NP	NP
Imipenem	4.7 ± 0.7	0.38 ± 0.07	8.1 × 104	NH	NC	NC	0.45	0.004	9.0 × 103
Aztreonam	NHa	NCb	NC	NH	NC	NC	—	—	—

^aNH, no measurable hydrolysis was detected after 2 h of incubation.

^bNC, not calculated.

^cData for GES-2 were reported in reference 25.

^dND, not determined due to very high K_m values.

^eNP, not provided in reference 25.

^f—, not hydrolyzed (the initial rate of hydrolysis was less than 0.001 μM⁻¹ s⁻¹).