What is the role served by the distal histidine in haemoglobin? The distal histi

Question

What is the role served by the distal histidine in haemoglobin? The distal histidine binds in an axial site and ensures the Fe remains in a low- spin state. The distal histidine stabilises the oxygen ligand in oxy-Hb through formation of a hydrogen bond from the imidazole ring. prevent formation of methaemoglobin The distal histidine triggers a conformational change upon binding to the Fe, binding affinity for oxygen. The distal histidine acts as an acid to protonate coordinated oxygen to render O The distal histidine acts as a soft ligand to stabilise the softer Fe(lI) state and O which is communicated through the Hb protein resulting in an increase irn it more labile.

Explanation / Answer

Ans : The distal histidine stabilises the oxygen ligand in oxy-Hb through formation of a hydrogen bond from the imidazole ring.

The distal histidine also acts as a gate for the ligand entry in alpha and beta subunits of hemoglobin.

It positions the oxygen atom between the nitrogen atom and the iron atom of the same imidazole ring , hence stabilizing it.

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