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[16] δ-Aminolevulinic acid dehydratase (Rhodopseudomonas spheroides)

1970; Academic Press; Linguagem: Inglês

10.1016/0076-6879(71)17181-9

1557-7988

David Shemin,

Porphyrin and Phthalocyanine Chemistry

Publisher Summary δ-aminolevulinic acid (ALA) dehydratase catalyzes the condensation of two molecules of ALA to a pyrrole, porphobilinogen, which is the aromatic precursor for porphyrins and other tetrapyrrole-like compounds. The formation of pyrrole from aminoketones requires an aldol condensation, the elimination of the elements of water from the carbon atom bearing the newly formed hydroxyl group and an adjacent carbon atom, and the formation of a Schiff base by the elimination of another molecule of water. The enzyme activity is determined by measuring the amount of porphobilinogen formed at 37° in a 3.0 ml reaction mixture containing 300 micromoles of Tris-HCl buffer, pH 8.5. A unit of enzyme activity is the amount of enzyme that produces 1 micromole of porphobilinogen in 60 minutes at 37°. Specific activity is defined as units of enzyme activity per milligram of protein. The pH optimum for the purified enzyme is about 8.5. The sulfhydryl nature of the enzyme is supported by the complete inhibition of the enzyme activity by p-chloromercuribenzoate at a concentration of 3.3 × 10-4 M.