A novel family VIII carboxylesterase hydrolysing third- and fourth-generation cephalosporins

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Table 1 Kinetic parameters for hydrolysis of p-nitrophenyl butyrate and cephalosporins (cephalothin, cefotaxime, and cefepime) by EstSTR1 and its mutant enzyme (S71A)

Substrates	k _cat (s⁻¹)		K_m (μM)		k _cat/K_m (M⁻¹ s⁻¹)
	Wild	S71A	Wild	S71A	Wild	S71A
p-nitrophenyl butyrate	297.12 ± 5.90	nh	65.62 ± 5.92	nh	4.52 ± 0.001 × 10⁶	nh
Cephalothin	4.63 ± 0.03 × 10⁻⁵	nh	16.58 ± 0.18	nh	2.78 ± 0.03	nh
Cefotaxime	1.57 ± 0.04 × 10⁻⁶	nh	0.90 ± 0.004^a	nh	1.67 ± 0.01	nh
Cefepime	1.63 ± 0.03 × 10⁻⁶	nh	0.19 ± 0.003^a	nh	8.48 ± 0.01	nh