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THE PATHWAYS FOR BI OSYNTHESIS OF TETRAPYRROLE. Oleg V. MOSIN Moscow State Academy of Fine Chemical Technology, Moscow, Vernadskogo prospect, 86 Tetrapyrrole biosynthesis comprises as well the formation of non-cyclic, open chain tetrapyrroles like bile pigments in animal tissue and phycobilins and phytochrome in the plant kingdom, as the synthesis of cyclic tetrapyrroles like heme in all kind of living cells, chlorophylls

in plants and corrins in certain microorganisms. From the early studies on heme biosynthesis the intermediates of the heme pathway and the corresponding enzymes are well known. The pathway starts with the condensation of glycin and succinyl-CoA by ALA-synthase (Neuberger, 1961; Jordan and Shemin, 1972) to form ALA, the first specific intermediate of all tetrapyrroles.

This pathway is called the Shemin-pathway. Subsequent condensation of two molecules of ALA leads to porphobilinogene, a step catalyzed by ALA-dehydratase (Shemin, 1972). The formation of the first cyclic tetrapyrrole structure is then performed by two enzymes, porphobilinogen deaminase and uroporphyrinogen III cosynthase (Bogorad, 1958 a,b) leading to uroporphyrinogen

III, one of the most common intermediates in the field of tetrapyrrole synthesis. The next step is then the decarboxylation of uroporphyrinogen III to coproporphyrinogen III by uroporphyrinogen decarboxylase. Oxidation of coproporphyrinogen III by coproporphyrinogen oxidase leads to protoporphyrinogen IX, which is subsequently oxidized by protoporphyrinogen oxidase, under certain circumstances also nonenzymatically

by oxygen. The last step before the branching into diffe¬rent heme-chromophores is the incorporation of Fe into the molecule by heme synthase, also called ferrochelatase. The intermediates of heme biosynthesis and the enzymes catalyzing the interconversions are shown in Fig. 1. The branching of this pathway, leading to the formation of corrins and phycobilins will be discussed in detail in one of the following chapters. As chlorophyll, the most spread biomolecule on earth, is

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