Porphyria

The porphyrias are inherited or acquired disorders of certain enzymes in the heme biosynthetic pathway (also called porphyrin pathway). They are broadly classified as hepatic porphyrias or erythropoietic porphyrias, based on the site of the overproduction and mainly accumulation of the porphyrins (or their chemical precursors).

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In humans, porphyrins are the main precursors of heme, an essential constituent of hemoglobin, myoglobin, and cytochrome.

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Deficiency in the enzymes of the porphyrin pathway leads to insufficient production of heme. This is, however, not the main problem; most enzymes?even when less functional?have enough residual activity to assist in heme biosynthesis. The largest problem in these deficiencies is the accumulation of porphyrins, the heme precursors, which are toxic to tissue in high concentrations. The chemical properties of these intermediates determine in which tissue they accumulate, whether they are photosensitive, and how the compound is excreted (in the urine or feces).

Enzyme: An enzyme (from Greek ?nsimo (??????), formed by ?n = at or in and simo = leaven or yeast) is a protein that catalyzes, or speeds up, a chemical reaction....

Heme: A hæm or heme is a metal-containing cofactor that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Although porphyrins do not necessarily contain iron, a substantial fraction of porphyrin-containing metalloproteins do in fact have heme a...

Porphyrin: A porphyrin is a heterocyclic macrocycle made from 3 pyrrole subunits and one pyrroline subunit, and linked on opposite sides through 4 methine bridges. The macrocycle, therefore, is more aromatic, than the related corrins or chlorins. The extensive conjugated system makes the compound chromatic, h...