TABLE 3.

Kinetic parameters of SME β-lactamases^c

Enzyme	kcat (s−1)			Km (μM)			kcat/Km (μM−1 s−1)			Relative kcat/km
	AMP	IMP	CTX	AMP	IMP	CTX	AMP	IMP	CTX	AMP	IMP	CTX
SME-1	58 ± 4	185 ± 5	NDa	590 ± 17	535 ± 27	ND	0.10	0.35	0.0064b	1	1	1
SME H105R	5.7 ± 0.8	1.1 ± 0.3	ND	185 ± 45	159 ± 52	ND	0.031	0.007	0.014b	0.3	0.02	2.2
SME H105W	45 ± 2	230 ± 7	ND	132 ± 17	442 ± 23	ND	0.34	0.52	0.0093b	3.4	1.5	1.5
SME H105Y	25 ± 9	566 ± 54	ND	150 ± 113	1801 ± 165	ND	0.17	0.31	0.0038b	1.7	0.9	0.6

^ak_cat and K_m not determined (ND) directly because it is assumed that K_m ≫ [S].

^bk_cat/K_m determined using v₀ = k_cat/K_m [E][S_o], where v_o is velocity, E is enzyme concentration, S₀ is initial substrate concentration.

^cAMP, ampicillin; IMP, imipenem; CTX, cefotaxime.