If curve 3 represents the binding of oxygen to normal hemoglobin, which curve re

Question

If curve 3 represents the binding of oxygen to normal hemoglobin, which curve represents the binding of oxygen to a mutant hemoglobin with multiple His -> Gly mutations in the central cavity? (Please justify your answer)

A. Curve 1

B. Curve 2

C. Curve 3

D. Curve 4

If curve 3 represents the binding of oxygen to normal hemoglobin, which curve represents the binding of oxygen to a mutant hemoglobin with surface Tyr -> Phe and His -> Arg mutations that abolish tetramer formation? (Please justify your answer)

A. Curve 1

B. Curve 2

C. Curve 3

D. Curve 4

Explanation / Answer

Curve 4 represents binding of oxygen to a mutant hemoglobin with multiple His -> Gly mutations in the central cavity, because this mutation will reduce the tetramer formation and breaking of salt bridge will result in lower saturation of oxygen. Histidine is the most important residue which stabilises the heme tetramer required for oxygen binding.

Curve 1 represents the binding of oxygen to a mutant hemoglobin with surface Tyr -> Phe and His -> Arg mutations that abolish tetramer formation. Tyrosine mutation with phenylalanine will enhance the affinity of haem for oxygen, and dependence of oxygen binding at pH will decrease by substitution of arginine at histidine. Therefore, at lower oxygen concentration, saturation will be higher asin curve 1.

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