Table 2.

Kinetic parameters in the presence of 50 mM NaHCO₃ at pH 7.0

Substrate	First phase			Second phase
	kcat, s−1	Km, μM	kcat/Km, M−1⋅s−1	kcat, s−1	Km, μM	kcat/Km, M−1⋅s−1
Penicillin G	109  ± 3	23  ± 0.4	(5 ± 1) × 106	—	—	—
Ampicillin*	143  ± 7	34  ± 4	(4.2 ± 0.6) × 106	—	—	—
Carbenicillin*	112  ± 14	92  ± 16	(1.2 ± 0.3) × 106	—	—	—
Oxacillin	1261  ± 27	29  ± 2	(4.3 ± 0.3) × 107	331  ± 4	101  ± 21	(3.3 ± 0.7) × 106
Cloxacillin	1533  ± 16	114  ± 22	(1.3 ± 0.3) × 107	129  ± 1	110  ± 8	(1.2 ± 0.1) × 106
Cephaloridine*	57  ± 14	374  ± 94	(1.5 ± 0.5) × 105	—	—	—
Cephalothin	8.3  ± 0.1	32  ± 2	(2.6 ± 0.1) × 105	—	—	—

^*In the absence of supplemental bicarbonate these substrates showed biphasic kinetics: ampicillin: k_cat1 = 174 ± 34 s⁻¹, K_m1 = 27 ± 8 μM, k_cat1/K_m1 = (6 ± 2) × 10⁶ M⁻¹⋅s⁻¹; k_cat2 = 245 ± 96 s⁻¹, K_m2 = 183 ± 30 μM, k_cat2/K_m2 = (1.3 ± 0.6) × 10⁶ M⁻¹⋅s⁻¹. Carbenicillin: k_cat1 = 200 ± 8 s⁻¹, K_m1 = 191 ± 10 μM, k_cat1/K_m1 = (1.0 ± 0.1) × 10⁶ M⁻¹⋅s⁻¹; k_cat2 = 121 ± 9 s⁻¹, K_m2 = 430 ± 36 μM, k_cat2/K_m2 = (2.8 ± 0.3) × 10⁵ M⁻¹⋅s⁻¹. Cephaloridine: k_cat1 = 38 ± 7 s⁻¹, K_m1 = 344 ± 78 μM, k_cat1/K_m1 = (1.1 ± 0.3) × 10⁵ M⁻¹⋅s⁻¹; k_cat2 = 30 ± 12 s⁻¹, K_m2 = 2046 ± 804 μM, k_cat2/K_m2 = (1.4 ± 0.8) × 10⁴ M⁻¹⋅s⁻¹.