Question

Some primitive animals have a hemoglobin that consists of two identical subunits. (A) Sketch an oxygen-binding curve for this protein. (B) What is the likely range of the Hill coefficient for this hemoglobin if the subunits were to show cooperative versus non-cooperative behavior?

Answer 1

A) Oxygen binds to the subunits of hemoglobin in lungs at partial pressure of oxygen being 13.3 kPa. The oxygen binding curve for hemoglobin is a sigmoid curve in which initially the oxygen binds weakly with first subunit of hemoglobin but after its binding a change in conformation of other subunits of hemoglobin occurs increasing their affinity to bind with oxygen. This is cooperative binding.

B) What is the likely range of the Hill coefficient for this hemoglobin if the subunits were to show cooperative versus non-cooperative behavior?

Archibald Hill analysed cooperative binding of oxygen with hemoglobin in 1910. His study gave the hill reaction to analyse the cooperative binding to multisubunit proteins like hemoglobin. Hill coefficient is the measure of degree of cooperativity and is denoted by nH.

nH = 1 for non - cooperative binding (this happens when there is no communication between subunits of protein)

nH > 1 for cooperative binding (Observed in hemoglobin when the binding of ligand to one subunit facilitates the binding to other subunits)