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Figure 9
A fragment of bovine trypsin from PDB structure 3unr that includes the residue His91 that is presented as doubly protonated. However, such an assignment of H atoms (gray) is in conflict with the neighboring peptide N—H group of Ser93.

IUCrJ
Volume 1| Part 3| April 2014| Pages 179-193
ISSN: 2052-2525
doi:10.1107/S2052252514005442