Which Nitrogen in Histidine is Protonated

Textbooks tend to report structures as relatively static, whereas advanced biochemistry texts explore structural tautomerism. In essence, the histidine imidazole sidecvhain may move around it's protons and electrons when pH is roughly equal to pKa. Thus, the side chain exists as two tautomers where the two nitrogens sort of “share“ the double-bond character and the proton. #ImidazolRing #Histidine #aminoAcid #protein #polypeptideChain #oligopeptide #NikolaysGeneticsLessons #polypeptide #peptide #disulfideBridges #covalentBounding #ionicBounding #hydrophobicInteraction #proteinStructure #proteinSequence #proteinFolding #aminoAcids #proteins #Polypeptides #hydrolysesSynthesis #condensationReaction #condensationSynthesis #peptides #globularProteins #fibrousProteins #Genetics