Table 1.

Properties of cysteine LacY mutants double labeled by Alexa 488 and Alexa 647 fluorophores

LacY mutantExtent of labeling, mol per mol of protein
NPG binding, % of binding to nonlabeled mutant
A488A647
R73C/S401C/WT0.60.698
R73C/S401C/C154G0.70.893
I164C/S375C/WT10.779
I164C/S375C/C154G0.80.893
  • Estimated from absorption spectra (see Materials and Methods).

  • Detected by direct sugar-binding assay based on Trp-NPG FRET as described in Materials and Methods (32).