title: 5-Aminolevulinic acid dehydratase: alkylation of an essential thiol in the bovine-liver enzyme by active-site-directed reagents.
abstract: 1. 5-Aminolevulinic acid dehydratase from bovine liver has been shown to be inactivated by 5-halolevulinic acids and 3-halolevulinic acids. 2. The substrate, 5-aminolevulinic acid, protects the enzyme from modification by 5-halolevulinic acids. 3. Using tritiated chlorolevulinic acids, it was shown that four of the subunits in the octameric enzyme are preferentially modified. 4. The susceptible enzyme group modified is an --SH group of a reactive cysteine at or near the active site. 5. Oxidized enzyme is not affected by either 5-chlorolevulinic acid or 3-chlorolevulinic acid. 6. Evidence is presented which suggests that 5-chlorolevulinic acid is acting as an active-site-directed reagent.
mesh_terms: D000478:Alkylation; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D003545:Cysteine; D006868:Hydrolysis; D066298:In Vitro Techniques; D007982:Levulinic Acids / Q000494:pharmacology; D008099:Liver / Q000378:metabolism*; D010084:Oxidation-Reduction; D000623:Porphobilinogen Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013438:Sulfhydryl Compounds; D014357:Trypsin
chemical_list: D007982:Levulinic Acids; D013438:Sulfhydryl Compounds; C013439:5-chloro-4-oxopentanoic acid; C029373:3-chlorolevulinic acid; D014357:Trypsin; D000623:Porphobilinogen Synthase; D003545:Cysteine