Purification and properties of δ-aminolevulinic acid dehydratase from radish cotyledons

Abstract

δ-Aminolevulinic acid dehydratase (5-aminolevulinate hydro-lyase, EC 4.2.1.24) was purified from greening radish cotyledons. The final product was homogeneous on polyacrylamide disc gel electrophoresis and had a molecular weight, estimated by gel filtration, of 282,000 daltons. The enzyme seems to require magnesium ion as well as sulfhydryl compounds for maximum activity. EDTA and a low concentration of zinc ion markedly inhibited the activity. The optimum pH was 8.0; the Km value for δ-aminolevulinic acid was 3.85×10−4m. Levulinic acid was a competitive inhibitor of the enzyme, with a Ki of 2.14×10−4M. These properties were compared with those of microorganism and animal δ-aminolevulinic acid dehydratases.