Why is Histidine Special? The Unique Role of a Versatile Amino Acid
                                
                                
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                                    6 min read                                
                            
                                Did you know that histidine is the only amino acid with a side chain that has a pKa close to physiological pH, enabling it to exist in both protonated and deprotonated states at a neutral pH? This unique characteristic is why histidine is special and so functionally versatile in biological systems.