PORPHYRINSPORPHYRINS

Synthesis of porphyrins occurs in Synthesis of porphyrins occurs in animals for haem production and in animals for haem production and in plants for chlorophyll production.plants for chlorophyll production.

STRUCTURESTRUCTURE

Porphyrins are cyclic tetrapyrroles in which the pyrrole Porphyrins are cyclic tetrapyrroles in which the pyrrole rings, conventionally designated as A, B, C and D, are rings, conventionally designated as A, B, C and D, are linked through their carbon atoms by methene (–CH=) linked through their carbon atoms by methene (–CH=) bridgesbridges**..

Porphyrins emit intense red fluorescence when Porphyrins emit intense red fluorescence when exposed to light at around 400 nm. Thus, exposed to light at around 400 nm. Thus, spectrofluorometric methods provide very spectrofluorometric methods provide very sensitive detection and quantification of sensitive detection and quantification of porphyrins porphyrins

The porphyrin isomers differ in the arrangement The porphyrin isomers differ in the arrangement of the side-chain substituents (e.g. acetyl and of the side-chain substituents (e.g. acetyl and propionyl in uroporphyrins; methyl and propionyl propionyl in uroporphyrins; methyl and propionyl in coproporphyrins) in coproporphyrins) **..

Porphyrins are differentiated by the kind and Porphyrins are differentiated by the kind and order of substitutes occupying the 8 peripheral order of substitutes occupying the 8 peripheral position of pyrole rings of porphyrins .position of pyrole rings of porphyrins .

Of many kinds of porphyrins found in nature, Of many kinds of porphyrins found in nature, only uroporphyrin caproporphyrin and only uroporphyrin caproporphyrin and protoporphyrin have clinical significance. protoporphyrin have clinical significance. **

SYNTHESIS SYNTHESIS **

In mammalian cells, haem synthesis occurs mostly in liver In mammalian cells, haem synthesis occurs mostly in liver and erythropoietictissues (the erythropoietic cells (80%) and erythropoietictissues (the erythropoietic cells (80%) and the liver parenchymal cells (20%))and the liver parenchymal cells (20%))

The biosynthetic pathway starts in the mitochondrion and, The biosynthetic pathway starts in the mitochondrion and, after passing through three cytoplasmic stages, re-enters after passing through three cytoplasmic stages, re-enters the mitochondrion for the final steps of haem formation. the mitochondrion for the final steps of haem formation.

Haemoproteins play very important roles in electron and Haemoproteins play very important roles in electron and oxygen transport, in the activation of oxygen or hydrogen oxygen transport, in the activation of oxygen or hydrogen peroxide and, finally, in hydrogen peroxide decompositionperoxide and, finally, in hydrogen peroxide decomposition

**

REGULATION OF HAEM SYNTHESIS **

Regulation of haem biosynthesis in the liver

Retroinhibition of hepatic ALAS1 activity via a negative feedback regulation mediated by the

free intracellular haem pool.

BIBLIOGRAPHY BIBLIOGRAPHY

* Puy, Hervé and Deybach, Jean-Charles. "* Puy, Hervé and Deybach, Jean-Charles. "Haem biosynthesis Haem biosynthesis and excretion of porphyrinsand excretion of porphyrins", [Documento en línea]. Gastrohep, ", [Documento en línea]. Gastrohep, online Resource for Gastroenterology, Hepatology and online Resource for Gastroenterology, Hepatology and Endoscopy. Dirección URL: Endoscopy. Dirección URL: <http://www.gastrohep.com/ebooks/rodes/Rodes_2_3_10.pd<http://www.gastrohep.com/ebooks/rodes/Rodes_2_3_10.pdf>. f>.

** ** King,King, Michael W. Ph.D. Michael W. Ph.D. Iron, Heme and Porphyrin Iron, Heme and Porphyrin MetabolismMetabolism, [Documento en línea]. The Medical , [Documento en línea]. The Medical Biochemistry Page. Dirección URL: Biochemistry Page. Dirección URL: <http://themedicalbiochemistrypage.org/heme-<http://themedicalbiochemistrypage.org/heme-

porphyrin.html>.porphyrin.html>.