Catalytic performances of the esterase pnbA-BS and its variants with single substitution of key residues in the substrate binding pocket^a.

Enzyme	e.e.p (%)	Conversion (%)	E
pnbA-BS	0.4 ± 0.5	90.5 ± 3.3	1.0
G105A	89.2 ± 1.3	37.6 ± 0.9	38.5
G106A		No activity
A107G	3.2 ± 0.9	96.9 ± 2.2	1.5
A107V	80.2 ± 1.2	35.6 ± 1.8	17.1
E188A	18.9 ± 0.3	66.6 ± 1.7	2.2
A190G	49.3 ± 1.9	33.2 ± 1.7	3.7
A190V	76.9 ± 2.1	58.5 ± 1.9	39.8
M193A	54.5 ± 1.6	54.3 ± 1.9	6.5
T326A	14.2 ± 0.6	88.5 ± 2.4	2.4
A330G	15.3 ± 0.4	88.7 ± 2.6	2.4
A330V	10.7 ± 1.7	79.9 ± 3.5	1.7
L331A	21.5 ± 1.3	62.7 ± 2.1	2.1
M358A	1.1 ± 0.6	92.0 ± 2.6	1.3
A400G	1.8 ± 0.7	98.0 ± 1.6	1.9
A400V	13.0 ± 1.6	82.8 ± 1.2	2.2
L403A	21.9 ± 0.8	64.6 ± 2.3	2.1
Host strain b	89.6 ± 1.4	4.5 ± 0.5	18.8

^aThe reaction mixture (10 ml) contained 100 mM d, l-menthyl acetate, 50 g l⁻¹ wet cells expressing pnbA-BS or its variant, 10% (v/v) ethanol, and 100 mM PBS buffer solution (pH 7.0). The reaction was conducted in an orbital shaker (600 rpm, 30 °C) for 6 h, in the meantime, the pH was constantly maintained by the titration of 1 M NaOH. Data present mean values ± SD from three independent experiments.

^bThe host strain was E. coli BL21(DE3) as the control without the expression of pnbA-BS or its variants.