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The following scheme summarizes the biosynthesis of porphyrins, with references by EC number and the OMIM database. The porphyria associated with the deficiency of each enzyme is also shown: Heme B biosynthesis pathway and its modulators. Major enzyme deficiences are also shown.
Metabolism [ edit ] In the typical porphyrin biosynthesis pathway, four molecules of porphobilinogen are concatenated by carbons 2 and 5 of the pyrrole ring (adjacent to the nitrogen atom) into hydroxymethyl bilane by the enzyme porphobilinogen deaminase , also known as hydroxymethylbilane synthase .
Other organisms produce ALA through a three enzyme pathway known as the C5 pathway. ALA is synthesized through the condensation of glycine and succinyl-CoA. In humans, transcription of ALA synthase is tightly controlled by the presence of Fe 2+-binding elements, to prevent accumulation of porphyrin intermediates in the absence of iron. There ...
The body requires porphyrins to produce heme, which is used to carry oxygen in the blood among other things, but in the porphyrias there is a deficiency (inherited or acquired) of the enzymes that transform the various porphyrins into others, leading to abnormally high levels of one or more of these substances. Porphyrias are classified in two ...
Porphobilinogen deaminase (hydroxymethylbilane synthase, or uroporphyrinogen I synthase) is an enzyme (EC 2.5.1.61) that in humans is encoded by the HMBS gene. Porphobilinogen deaminase is involved in the third step of the heme biosynthetic pathway.
X-linked sideroblastic anemia or "X-linked dominant erythropoietic protoporphyria", associated with ALAS2 (aminolevulinic acid synthase), has also been described.X-linked dominant erythropoietic protoporphyria (XDEPP) is caused by a gain of function mutation in the ALAS2 (5-aminolevulinate synthase) gene; that gene encodes the very first enzyme in the heme biosynthetic pathway.
Acute intermittent porphyria (AIP) is a rare metabolic disorder affecting the production of heme resulting from a deficiency of the enzyme porphobilinogen deaminase. It is the most common of the acute porphyrias. [1] [2] [3]
Aminolevulinic acid dehydratase (porphobilinogen synthase, or ALA dehydratase, or aminolevulinate dehydratase) is an enzyme (EC 4.2.1.24) that in humans is encoded by the ALAD gene. [ 5 ] [ 6 ] Porphobilinogen synthase (or ALA dehydratase , or aminolevulinate dehydratase ) synthesizes porphobilinogen through the asymmetric condensation of two ...