TABLE 3.

Amino acid sequence changes and DHFR characteristics of selected CP1015 transformants

Isolate	Amino acid at positiona:																		MIC (mg/liter)	IC50 (μM)	Km (μM)b		Specificity constantc
	14	16	20	26	53*	60	70	74	78	81	91	92	94	100*†	120	135	147	149			DHF	NADPH
ATCC 49619		V																	4	0.05	3.9 (0.83)	17.8 (4.4)	0.024
CP1015	E	L	E	H	M	K	P	I	A	Q	Q	D	E	I	H	L	F	A	4	0.09	3.1 (0.48)	18.2 (3.2)	0.014
720/T1	D	V	D				S	L		H	H	A	D	L		F	S	T	512	2.9	9.2 (3.3)	30.7 (7.9)	0.09
720/T2		V	D				S	L		H	H	A	D	L					256	1.4	12.6 (3.3)	21.9 (5.2)	0.04
1802/T1		V	D	Y	I	Q	S		T			A		L	Q	F	S	T	512	13.7	14.3 (2.3)	29.0 (4.4)	0.026
1802/T2		V	D	Y	I	Q	S		T			A		L					512	10.1	24.1 (8.6)	52.7 (23.7)	0.007
R12/T1									T			A		L	Q	F	S	T	256	2.1	15.2 (2.8)	20.3 (4.7)	0.016
R12/T2												A		L					128	4.2	27.7 (9.7)	35.1 (11.4)	0.0063

^a*, trimethoprim binding site in the DHFR of E. coli K-12; †, NADPH binding site in the DHFR of E. coli K-12 (as reported by Dale et al. [4, 5]). 

^bValues in parentheses are standard errors. 

^cV_max/K_m (μM).