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reading 2 - Many biosynthesis involves regioselective...

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Many biosynthesis involves regioselective chlorination by flavin-dependent halogenases. Ex. Tryptophan chlorinated by tryptophan 7-halogenase (PrnA). First tryptophan and flavin adenine dinucleotide (FAD) are separated and bound by distinct enzyme modules. FAD is conserved in halogenases (flavin-dependent monooxygenases). Proposal: FADH2 reacts with O2 to make peroxyflavin, then decomposed by Cl. The resulting HOCL activates Original Proposal: Metal-dependent haloperxoidases : 1. Heme-iron-dependent enzymes. 2. Vanadium- dependent enzymes. Both form a metal-bound hydrogen peroxide that reacts with halide ions to produce a metal bound hypohalite ion. This ion dissociates from the metal as hypohalous acid. In solution it reacts with substrate. Problem: the above halogenatiion lacks regioselectivity and substrate specificity. Discovery: perhydrolases are not involved in halometabolite biosynthesis. a new halgogenase was reported by Dairi et al. identifying the gene for the chlorinating enzyme in chlorotetracycline biosynthesis.
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