, Volume 1, Issue 1, pp 129-131

On the structure of histidine and its role in enzyme active sites

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A structural refinement is proposed for the mechanistic details of the action of the serine proteases. The proposal involves ring flipping of the imidazole function of the histidine side chain as a vehicle for proton transfer. The geometric feasibility of this motion is established by molecular graphics analysis of the crystal structure ofα-chymotrypsin. It is suggested that the shape of histidine is as important as its pK a for its function at the active sites of enzymes.