Raman spectra of ribonuclease A in D2O solution at various pD values have been studied with special attention to the N-deuterated imidazolium ring vibration at 1408 cm-1, the SO4(2-) symmetric stretching vibration at 984 cm-1, the amide I' band, and the tyrosine doublet. Concomitant decrease and increase in the intensities of the 1408- and 984-cm-1 bands in the pD range between 5 and 7 indicate that a sulfate anion is actually hydrogen bonded to an imidazolium ring of a histidine residue located in the interior of the molecule. The mechanism of the sulfate desorption has been compared with that on heat denaturation.
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Harada et al. (1982) studied this question.