Table 3.

Amino acid sequence changes and DHFR characteristics of selected CP1015 transformants

IsolateAmino acid at positiona:MIC (mg/liter)IC50(μM)Km(μM)bSpecificity constantc
1416202653*6070747881919294100*120135147149DHFNADPH
ATCC 49619V40.053.9 (0.83)17.8 (4.4)0.024
CP1015ELEHMKPIAQQDEIHLFA40.093.1 (0.48)18.2 (3.2)0.014
720/T1DVDSLHHADLFST5122.99.2 (3.3)30.7 (7.9)0.09
720/T2VDSLHHADL2561.412.6 (3.3)21.9 (5.2)0.04
1802/T1VDYIQSTALQFST51213.714.3 (2.3)29.0 (4.4)0.026
1802/T2VDYIQSTAL51210.124.1 (8.6)52.7 (23.7)0.007
R12/T1TALQFST2562.115.2 (2.8)20.3 (4.7)0.016
R12/T2AL1284.227.7 (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 ofE. coli K-12 (as reported by Dale et al. [4, 5]).

  • b Values in parentheses are standard errors.

  • c Vmax/Km(μM).