I believe the appropriate answer is Glutamic acid to valine. Sickle cell disease is a blood condition prevalent in people of African and in the tribal people of India. The sickle cell mutation reflects a single change in the amino acid building blocks of oxygen transport protein (hemoglobin). This protein has two sub units the (alpha and beta sub unit), In people with sickle cell the alpha sub-unit is normal. However the beta sub unit has the amino acid Valine at position six instead of the glutamic acid that is present in normal cases