Titration curves of histidine

Fig. 6.9. Titration curve of histidine. The ionic species that predominates in each region is shown below the graph, pi is the isoelectric point (at which there is no net charge on the molecule).

Shindo, H., Hayes, M. B., and Cohen, J. S., 1976, Nuclear magnetic resonance titration curves of histidine ring protons. A direct assignment of the resonance of the active site histidine residues of ribonuclease, /. Biol. Chem. 251 2644. 

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