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Delta-aminolevulinic acid dehydratase This entry represents porphobilinogen (PBG) synthase (PBGS, or 5-aminoaevulinic acid dehydratase, or ALAD, ), which functions during the second stage of tetrapyrrole biosynthesis. This enzyme catalyses a Knorr-type condensation reaction between two molecules of ALA to generate porphobilinogen, the pyrrolic building block used in later steps. The structure of the enzyme is based on a TIM barrel topology made up of eight identical subunits, where each subunit binds to a metal ion that is essential for activity, usually zinc (in yeast, mammals and certain bacteria) or magnesium (in plants and other bacteria). A lysine has been implicated in the catalytic mechanism. The lack of PBGS enzyme causes a rare porphyric disorder known as ALAD porphyria, which appears to involve conformational changes in the enzyme.
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Jiyao W et al.(2023). "The conserved domain database in 2023.",