Figure 3.

The K minus BR difference spectra of unlabeled (dotted lines) and [3-¹⁸O]threonine-labeled (solid lines) BR in the 3,530- to 3,350-cm⁻¹ region. The sample was hydrated with D₂O. The window-tilting angles (φ₀) are 0° (a), 17.8° (b), 35.7° (c), and 53.5° (d). One division of the y axis corresponds to 0.001 absorbance unit. Two peak pairs, 3,480 (+)/3,462 (−) cm⁻¹ and 3415 (+)/3402 (−) cm⁻¹, are able to be assigned for the O-H stretching vibrations of threonine side chains. Diff. Abs., difference absorbance.