Abnormal Hemoglobin Derivatives| Biochemistry

The following points highlight the three major derivatives of abnormal hemoglobin. The derivatives are: 1. Met-hemoglobin 2. Sulfhemoglobin 3. Carboxyhemoglobin.

Derivative # 1. Met-hemoglobin:

a. This is an oxidized hemoglobin (ferrous iron is oxidized to ferric iron). Oxygen is in firm combination.

b. It is incapable of functioning as an oxy­gen carrier. Cyanosis usually develops when the concentration of it reaches 3 grams per 100 ml of blood.

c. Met-hemoglobin in normal erythrocytes is 0.4 per cent of the total hemoglobin. With very high concentration, the cells may be injured, destroyed and may be liberated into the plasma along with hemoglobin and excreted in the urine.

Causes of met-hemoglobin:

i. Drugs and other toxic agents: Nitrites, chlorates etc.

ii. Other hemolytic agents.

iii. Enterogenous cyanosis: Due to excessive production and absorption of nitrites from the intestine.

iv. Congenital: One form is characterized by the abnormality in the molecular structure of the globin component. In another type, there is the deficiency of diaphorase en­zyme system which catalyzes reduction of met-hemoglobin to hemoglobin.

Derivative # 2. Sulfhemoglobin:

a. Reduced hemoglobin combines with hy­drogen sulphide to form sulfhemoglobin.

b. Sulfhemoglobinemia is an unusual con­dition which occurs chiefly as a result of the action of nitrites and coal tar prepara­tions in the presence of excessive amounts of sulfur.

c. It is also observed in subjects with marked constipation in the presence of nitrite-pro­ducing bacteria in the intestine.

d. Cyanosis usually occurs when the concen­tration of sulfhemoglobin reaches 3 to 5 grams per 100 ml of blood.

Derivative # 3.Carboxyhemoglobin:

a. It is formed as a result of the combination of carbon monoxide with the iron in the hemoglobin molecule.

b. It has a bright, cherry-red colour.

c. It is formed by the excessive exposure to artificial illuminating gas and to automo­bile exhaust gases in closed or poorly ven­tilated rooms.