Table 1.

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

LacY mutant	Extent of labeling,† mol per mol of protein		NPG binding,‡ % of binding to nonlabeled mutant
	A488	A647
R73C/S401C/WT	0.6	0.6	98
R73C/S401C/C154G	0.7	0.8	93
I164C/S375C/WT	1	0.7	79
I164C/S375C/C154G	0.8	0.8	93

^†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).