5‐Aminolevulinic Acid Dehydratase

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Abstract
5-Aminolevulinic acid dehydratase from bovine liver was inactivated by 5-halolevulinic acids and 3-halolevulinic acids. The substrate, 5-aminolevulinic acid, protects the enzyme from modification by 5-halolevulinic acids. Using tritiated chlorolevulinic acids, it was shown that 4 of the subunits in the octameric enzyme are preferentially modified. The susceptible enzyme group modified is an -SH group of a reactive cysteine at, or near, the active site. Oxidized enzyme is not affected by 5-chlorolevulinic acid or 3-chlorolevulinic acid. Evidence is presented which suggests that 5-chlorolevulinic acid is acting as an active-site-directed reagent.