Page 30 - General Biochemistry

• The symptoms are cyanosis (blue skin) and dyspnoea (labored breathing).

Importance of methemoglobin
Met-hemoglobin can be used to overcome cyanide poisoning. By injecting met-

hemoglobin it combines with cyanide to form cyanomethemoglobin
preventing cyanide poisoning.
• The defect lies both in α and β chains. This is due to replacement of
histidine residue in the 58th position in α chain and 63rd position in β chain.
• Due to this replacement, the iron (Fe) present in the ferrous state is oxidized
to ferric state.
• This ferric iron cannot bind oxygen. Therefore the oxygen carrying capacity
is disrupted leading to anemia and hypoxia (low O2 to tissues).

5. Carboxyhemoglobin
• Oxy-hemoglobin can bind to carbon monoxide (CO). Even normal, non-
oxygenated hemoglobin can bind with CO to form carboxyhemoglobin. [Hb
+ CO → HbCO].
• CO has got an affinity of 200 times more than that of O2 towards Hb.
• Even if there is a little amount of CO in air, it can displace oxyHb to form
carboxyHb.
• Due to this there will be tissue hypoxia because the oxygen binding capacity
is reduced and there is also reduced O2 releasing capacity i.e. it cannot
release O2 though it may be bounded to O2.

• City dwellers have at least 1% of carboxyhemoglobin which can increase to
8% depending upon the pollution. Over traffic can increase carboxyHb to
40% which leads to death.

• Clinically such patients show cherry red colour of skin.
• CO poisoning can be treated if high amount of O2 is provided continuously

at high pressure, then at such high concentrations and pressure HbCO is
dissociated forming HbO2 + CO.
• When treatment continues for 2 hours CO is expelled out.

6. HbS or Sickle Cell Hemoglobin
• Sickle cell hemoglobin (HbS) arises due to the defect in β chain in which

glutamic acid present at the 6th position is replaced by valine.
• Valine is also present naturally at position one.
• These two valine residues form hydrophobic interaction producing a sticky

patch on HbS.

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