Porphyrin

Porphyrin is a group of organic compounds, many of which play significant roles in biochemistry. The most well-known porphyrins are heme, the pigment in red blood cells, and chlorophyll, the pigment in plants that is responsible for photosynthesis.

Structure

Porphyrins are heterocyclic macrocycles composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (=CH−). Porphyrins are aromatic. They have a deep color and are highly conjugated. They are also stable, although they can be degenerated by strong acids or bases.

Biosynthesis

Porphyrins are synthesized in a series of steps from the simple precursors glycine and succinyl-CoA. The process begins with the formation of delta-aminolevulinic acid, which is then converted to porphobilinogen. Four molecules of porphobilinogen are then combined to form a linear tetrapyrrole, which is cyclized to form uroporphyrinogen III. This molecule is then converted to coproporphyrinogen III, which is decarboxylated to form protoporphyrinogen IX. Finally, protoporphyrinogen IX is oxidized to form protoporphyrin IX, the final product of the pathway.

Role in biology

Porphyrins play a crucial role in biology. They are the core component of many important biological molecules, including heme, chlorophyll, and vitamin B12. Heme, for example, is a component of hemoglobin, the molecule that carries oxygen in the blood. Chlorophyll, on the other hand, is essential for photosynthesis in plants.

Medical significance

Abnormalities in porphyrin metabolism can lead to a group of rare genetic disorders known as porphyria. These disorders are characterized by an accumulation of porphyrins or porphyrin precursors in the body, leading to a variety of symptoms including skin sensitivity to sunlight, abdominal pain, and neurological complications.

See also

• Heme
• Chlorophyll
• Vitamin B12
• Porphyria

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