Structure of Haemoglobin

STRUCTURE OF HAEMOGLOBIN

1 RBC consists of approximately 250 million Hb molecules

STRUCTURE OF HB- GENERAL

Haemoglobin is a hemoprotein only found in the cytoplasm of RBC transports O2 and CO2 between lungs and various tissues normal concentration of Hb in the blood: adult males 135 – 175 g/L adult females 120 – 168 g/L

STRUCTURE

Made up of heme + Globin

4 polypeptide Subunits

Heme group Porphyrin ring Ferrous iron

Globin chain 2 Alpha Chains 2 Beta chains

HEME STRUCTUREHEME IS A METALOPORPHYRINE(CYCLIC TETRAPYRROLE)

Heme contains: conjugated system of

double bonds → red colour

4 nitrogen (N) atoms

1 iron cation (Fe2+)→ bound in the middle of tetrapyrrole skeletal by coordination covalent bonds

methine bridge pyrrole ring

PROPERTIES OF IRON IN HEME

• Coordination number of iron in heme = 6

6 bonds:• 4x pyrrole ring

(A,B,C,D)• 1x link to a protein• 1x link to an oxygen

STRUCURE OF GLOBINGlobin: Four polypeptide chains in one

molecule of Hb Adult Hb(Hb A) has four

polypeptide chains 2 α variety & 2 β variety α consists of 141 AA and β 146

AA HbA is symbolised α2 β2 Other types of normal Hb: o Hb F (α2ɣ2) o Hb A2(α2δ2) (2.5% of HbA)

STRUCURE OF HAEMOGLOBIN

• With each of 4 polypeptide chains one haem molecule is attached

• Each haem part contains one iron molecule• With each iron molecule, one molecule O2 can

combine• With each molecule of Hb, 4 molecules of O2

can combine• Structure changes slightly during binding &

release of O2

BOND OF HAEMOGLOBIN

Bonds between α1 & β2 chains are weaker than α1, β1.

α1 & β2 are able to move and get twisted, allowing change between tense and relaxed form.

Tense form is present in deoxygenated Hb Β chains move away from each other 2,3

DPG binds here. Presence of 2 3 DPG increases O2

delivery to tissues Relaxed form is present in Oxygenated

Hb. 2 3 DPG expelled allowing further O2

binding.

Quaternary structure of deoxy- and oxyhemoglobin

T-state (deoxy-state) R-state (oxy-state)

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