Lecture 15

• Haemoglobin -> polypeptide. Haem -> red pigment. Globin is made up of 4 polypeptide chains: 2 alpha and 2 beta.

• Each alpha has 141 amino acids and each beta has 146 amino acids. 2 alpha = 141+141. 2 beta = 146+146.

• Haemoglobin is represented by Hb. • HbA (alpha2beta2) = adult haemoglobin.• Haem -> containing iron, seen in the ferrous (Fe2+). Each Fe2+ combines

loosely and reversibly with oxygen. • Combination of heme with oxygen is called as oxygenation. Not oxidation. • After combining Fe2+ , it stays in its Fe2+, does not go to Fe3+. • This oxygen would be carried in molecular oxygen form. It doesn’t change

to ionic oxygen. • Each polypeptide chain, 1, 2, 3, 4 combines with one heme molecule. Each

heme has one Fe2+. • 1 hemoglobin molecule, made up of 4 polypeptide chains, bind to one

heme molecule each, one heme has a Fe2+. • 4 oxygen molecules, 8 atoms of oxygen, each haemoglobin molecule

carries. • The affinity of one heme for first oxygen is low compared to affinity of

fourth heme for fourth oxygen. • Binding of first heme to oxygen Increases affinity of second heme for

oxygen, this further increases the affinity of third heme for third oxygen and later the fourth one. The fourth heme has the highest affinity for the fourth oxygen.

• The increased in affinity shows a sigmoid curve. • Binding of heme to 1 oxygen molecule is rapidly seen at a rate of 0.01

second. Dissociation is rapid too. • Oxyhemoglobin – Hb+ 02 -> HbO2. There is an affinity. The affinity

depends on some factors = pH, temperature, concentration of 2,3 DPG = diphosphoglycerate (byproduct of glycolysis).

• Carbaminohemoglobin: CO2 + HbNH2 -> HbNH COOH (carbaminohemoglobin).

• Reduced oxygen, reduced deoxygenated haemoglobin.• Carboxy Haemoglobin/Carbon monoxy Haemoglobin. The affinity of

Carbon monoxide to haemoglobin is 250 times more than affinity of oxygen towards Hb. • Methaemoglobin: when reduced or oxyhemoglobin is exposed to certain

drugs/agents or some oxidizing agents, Fe2+ will be oxidized to Fe3+. That results in methaemoglobin = HbOH. It has some disadvantages:

• Methaemoglobin cannot unite reversibly with oxygen. It cannot convert into normal haemoglobin.

• When methaemoglobin is seen in large quantities in circulation, it mimics cyanosis -> the blue coloration of the skin. This methaemoglobin is a dark colored pigment.

• Normally you can also see the conversion of haemoglobin to methaemoglobin , rare cases.

• The RBCs have some enzymes = NADH methaemoglobin reductase system , responsible to convert methaemoglobin back to normal haemoglobin. Congenital absence of this enzyme leads to methaemoglobin blood condition (methaemoglobinemia) which is fatal.

• Some factors involved in synthesis of haemoglobin:• 1) role of proteins – decrease amount of protein intake, lead to lack of

globin. Not the haem. 0.33%• 2) role of vitamins -• 3) role of minerals (iron, copper, cobalt)• Iron: helps in formation of heme portion. • Copper: absorption, transport and utilization of iron. • Cobalt: is responsible for the manufacture of Vitamin B12 Balamin.

Vitamin B12 responsbie for formation of erythropoietin. The erythropoietin hormone responsible for development of RBCs.

• Life of RBCs: 120 days. After that, the old/worn out RBC will be destroyed by the reticulo-endothelial system. Tissue-macrophage system.

• RBC -> entering the tissue-macrophage system. We have two parts within the haemoglobin = dividing into the heme part and the globin part. The heme part – Fe2+, a part of Fe2+ has been divided and this Fe2+ combines with tissue protein called apoferritin (binds and stores iron). Apoferritin is a tissue protein that binds and stores iron in the form of ferritin. Ferritin is store in the liver.

• The other part of Fe2+ is oxidized to Fe3+ = leading to the bile pigments (bilverdin and bilirubin).

• Globin just goes into the amino acid pool • Haemoglobin: some physical and chemical differences in the globin part

itself. • HbA (alpha2beta2) predominantly seen = adult haemoglobin. Alpha has

141 aa. Beta has 146 aa.• HbA2 (alpha2delta2). Alpha has 141 aa. Delta has 146 aa. 10 aa within

this 146 aa are going to differ from beta. It is not considered an abnormal haemoglobin.

• HbA starts in fetus; 5 months (20 weeks) of intrauterine life till bone morrow becomes the hemopoeitic agent.

• HbF – fetal haemoglobin. HbF (alpha2gamma2). Each alpha has 141 amino acids. Gamma also has 146 amino acids, but 37 amino acids are going differ from beta. HbF has a high affinity towards oxygen, because of poor binding of 2,3 DPG to gamma polypeptide chain.

• It can easily combine with oxygen. • HbF predominates until 2-3 months after birth -> has to be synthesized to

HbA. HbF has to disappear after 2-3 months. If HbF persists to 4-6 months, this is a disease called Thalassemia. If problem with alpha chain, this is alpha (alpha cells lacking) thalassemia. If beta cells lacking, beta thalassemia.

• Among beta thalassemia, what is the most common and why?