porphobilinogen

A porphyrin precursor of porphyrinogens, porphyrins, and heme; found in the urine in large quantities in cases of acute or congenital porphyria.

- p. synthase a liver enzyme catalyzing the formation of p. and water from two molecules of δ-aminolevulinate, an important reaction in porphyrin biosynthesis; inhibited by lead in cases of lead poisoning; a deficiency of this enzyme results in elevated levels of δ-aminolevulinate and results in neurologic disturbances. SYN: δ-aminolevulinate dehydratase.

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por·pho·bi·lin·o·gen .pȯr-fō-bī-'lin-ə-jən n a dicarboxylic acid C₁₀H₁₄N₂O₄ that is derived from pyrrole, that is found in the urine in acute porphyria, and that on condensation of four molecules yields uroporphyrin and other porphyrins

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n.

a pigment that appears in the urine of individuals with acute porphyria, causing it to darken if left standing.

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por·pho·bi·lin·o·gen (por″fo-bĭ-linґə-jən) the immediate precursor of the porphyrins, a pyrrole ring with acetyl, propionyl, and aminomethyl side chains; four molecules of porphobilinogen are condensed to form one molecule of uroporphyrinogen III, which is then converted successively to coproporphyrinogen III, protoporphyrin IX, and heme. Porphobilinogen is produced in excess and excreted in the urine in acute intermittent porphyria and several other porphyrias. Abbreviated PBG.