Question

Histidine often shows up as a key player in enzymatic reaction mechanisms and likewise often serves as one of the catalytic residues in the active site of many different types of enzymes.  Suggest several reasons why histidine has this versatility.  What sorts of useful chemical properties does Histidine possess that enable it to facilitate enzymatic reactions?

Answer 1

Histidine is one of the amino acids which is a key player for enzymatic reactions.

It contains -amino group (-NH₃)⁺, carboxylic acid (-COOH) and imidazol group. Imidazol side chain consists of partially protonated thus it belongs to positively charged amino acid category at physiological pH. Moreover, imidazol side chain in Histidine serves as a ligand in metalloprotein and it is a part of catalytic site in a certain enzymes.

The imidazol part of histidine able to switch between protonated and deprotonated states which allows histidine to take part in acid base catalytic reaction.

For example, Histidine is important in haemoglobin where imidazol part is catalytic residue which binds iron.