Question

Explain what happens to the imidazole side chain of histidine in a buffer of pH 4.0 and at pH 10.2.

Answer 1

Histidine, an essential amino acid, has as a positively charged imidazole functional group. The imidazole makes it a common participant in enzyme catalyzed reactions. The unprotonated imidazole is nucleophilic and can serve as a general base, while the protonated form can serve as a general acid.