Fig. 4.
Reaction-induced FT-IR spectra, associated with the S2-minus-S1 transition in PSII. The box highlights the amide carbonyl (CO) stretching region. The data were acquired after the addition of (A) 100 mM NaCl in 0.4 M sucrose buffer, pH 7.5 or after the addition of (B) 100 mM NaCl in 0.4 M trehalose buffer, pH 7.5. In (C), a representative baseline is shown. The spectra are averages of data obtained from (A) 14, (B) 12, and (C) 14 samples. The y-axis tick marks represent 1 × 10-4 absorbance units. See Materials and Methods for more details.