TABLE 3.

Steady-state kinetic parameters of wild-type OXA-57 and the D170N and K232N mutant enzymes

Substrate	Enzyme	Km (μM)a	kcat (s−1)a	kcat/Km (s−1 M−1)
Nitrocefin	WTc	17.9 ± 2.1	63.0 ± 7.5	3.51 × 106
	D170N	50.4 ± 13	79.5 ± 21	1.58 × 106
	K232N	13.2 ± 3.3	29.7 ± 7.4	2.24 × 106
Ampicillin	WT	71.9 ± 9.6	0.54 ± 0.1	7.54 × 103
	D170N	38.9 ± 2.7	2.12 ± 0.2	5.44 × 104
	K232N	157 ± 26	1.42 ± 0.2	8.98 × 103
Penicillin G	WT	29.5 ± 5.1	0.40 ± 0.1	1.36 × 104
	D170N	56.3 ± 8.5	0.61 ± 0.1	1.07 × 104
	K232N	46.6 ± 11	0.75 ± 0.2	1.60 × 104
Cloxacillin	WT	28.7 ± 4.2	0.51 ± 0.1	1.79 × 104
	D170N	166 ± 16	1.12 ± 0.1	6.69 × 103
	K232N	180 ± 29	1.04 ± 0.2	5.77 × 103
Oxacillin	WT	40.7 ± 6.1	1.23 ± 0.2	3.02 × 104
	D170N	37.2 ± 2.5	2.37 ± 0.2	6.37 × 104
	K232N	194 ± 47	3.07 ± 0.8	1.57 × 104
Piperacillin	WT	21.3 ± 3.8	2.11 ± 0.4	9.90 × 104
	D170N	22.1 ± 1.1	5.7 ± 0.3	2.58 × 105
	K232N	9.48 ± 1.2	4.31 ± 0.5	4.55 × 105
Cephalothin	WT	163 ± 11	0.28 ± 0.1	1.73 × 103
	D170N	100 ± 7.5	0.86 ± 0.1	8.59 × 103
	K232N	55.4 ± 3.9	0.65 ± 0.1	1.17 × 104
Cephaloridineb	WT	97.9 ± 15	13.0 ± 1.9	1.33 × 105

^aValues are means±standard errors of the means (n = 3).

^bAssay was not performed for the D170N and K232N mutant enzymes.

^cWT, wild-type OXA-57.