Porphyrin Biosynthesis Starts with the Condensation of Glycine and Succinyl-CoA

Porphyrin Biosynthesis Starts with the Condensation of Glycine and Succinyl-CoA 

Early isotope tracer experiments by David Shemin permitted the elucidation of the formation of the immediate precursor of the porphyrin needed for the cytochromes and for hemoglobin. These studies indicated that the glycine methylene carbon and nitrogen were incorporated along with both carbons of acetate. Subsequent enzymatic studies in both bacteria and animals revealed a condensation reaction between succinyl-CoA and glycine to yield 5-amino-levulinate and C02 (presumably by way of an enzyme-bound /3-keto acid, a-amino-/3-ketoadipate) (fig. 22.13). 

The pyrrole monomer porphobilinogen arises from the condensation of two molecules of S-aminolevulinate with the ions of two water molecules. This reaction is catalyzed by S-aminolevulinate dehydrase. Condensation of four porphobilinogen molecules yields the branchpoint compound in tetrapyrrole synthesis, uroporphyrinogen III. This is a complex reaction requiring two enzymes Uroporphyrinogen I synthase, which catalyzes a head-to-tail condensation 

Derivatives of porphyrins are coenzymes in a number of oxidation-reduction reactions (see chapters 10, 14, and 15). 

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