Difference spectrum due to melibiose interaction. (A) (Solid line) ATR-FTIR difference spectrum of a film of MelB in D2O in 20 mM MES, 100 mM KCl, 10 mM NaCl, 10 mM melibiose, pH 6.6; minus the film in 20 mM MES, 100 mM KCl, 10 mM NaCl, pH 6.6. (Shaded line) The same difference in H2O. (B) (Solid line) Deconvoluted spectrum of the difference in D2O shown in panel A. (Shaded line) Deconvoluted spectrum of the difference in H2O shown in panel A. The wavenumbers that coincide in both spectra are in bold.