The determination of the pKa of histidine residues in proteins by Raman difference spectroscopy

Kwok To Yue, Minghe Lee, Jie Zheng, Robert Callender

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Sensitive Raman difference spectroscopy was used to monitor the protonation and deprotonation of histidine residues in apo-transferrin. We have shown previously that the behavior of small molecules and/or small molecular groups bound to proteins or other large macromolecules can be studied by Raman difference spectroscopy (Yue, K.T. et al. (1989) J. Raman Spectrosc. 20, 541-545). Using this method, we have measured the Raman difference spectra of human transrferin at different pH values with respect to pH 8.9, titrating its various histidine residues. About 12±2 of the 19 residues were titrated. The pH difference spectrum of transferrin obtained is very similar to that of histidine in solution, but with clear differences in the 1200-1400 cm-1 region. A titration curve with pKa of 6.08 ± 0.01 fit the data of histidine in solution and a value of 6.56 ± 0.02 was found for the average value of the 12 histidine residues inside transferrin. The technique has enough sensitivity at present to monitor a single histidine residue in a 130 kDa molecule and to determine the titration curve of one residue in a 40 kDa protein.

Original languageEnglish (US)
Pages (from-to)296-302
Number of pages7
JournalBiochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
Issue number2
StatePublished - Jun 24 1991
Externally publishedYes


  • Chemical state
  • Ionization state
  • Methodology
  • Raman spectroscopy

ASJC Scopus subject areas

  • Molecular Biology
  • Structural Biology
  • Biophysics
  • Biochemistry


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