 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 1]](gr0963fig1mag.jpg)
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Figure 1
(a) Tetrapyrrole biosynthesis is an ancient and essential pathway. The first common intermediate is 5-aminolevulinic acid (ALA). One molecule of ALA condenses with a second one to form the monopyrrole porphobilinogen in a reaction catalyzed by the metalloenzyme porphobilinogen synthase (PBGS). The PBGS-catalyzed reaction is the first common step in the biosynthesis of the tetrapyrrole cofactors. (b) The PBGS-catalyzed reaction involves the formation of one carbon–carbon bond (dotted line) and one carbon–nitrogen bond (dashed line), as well as the loss of four protons and two O atoms (shown in black). The only known reaction intermediate is a Schiff base formed between an active-site lysine and C4 of the ALA molecule whose fate is the propionyl-containing half of porphobilinogen (P-side ALA, shown in turquoise). For mammalian PBGS, the ZnII is implicated in the binding and reactivity of the ALA molecule whose fate is the acetyl-containing half of porphobilinogen (A-side ALA, shown in red). Little else is known about the order of chemical events or the active-site residues that mediate the chemical transformations. |
![[Figure 1]](gr0963fig1.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
