Page 25 - Clinical biochemistry

Composition of Hemoglobin

Heme
• It is an iron-porphyrin compound.
• It is the prosthetic group embedded in the packet like structure formed by
folding of the hemoglobin tertiary structure.

Porphyrin
• Porphyrin is a complex compound with a tetrapyrrole ring structure.
• Pyrrole is a heterocyclic compound having the following structure.

• This porphin is substituted by different groups at positions numbered from
1-8 to form the porphyrin.

• Depending upon the groups (methyl, acetyl, propyl, butyl or venyl) present
on these positions different types of porphyrins are identified.

Properties of porphyrins
1. They act both as acids (-COOH) and bases (-NH2).
2. Their isoelectric pH is between 3-4.5.
3. Porphyrins are fluorescent and coloured due to the presence of alternating
double bonds.
4. Porphyrinogens are colourless.

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