d-Aminoacylase has been purified 144-fold to electrophoretic homogeneity by ammonium sulfate fractionation, DEAE-Toyopearl and affinity column chromatographies, and Sephadex G-100 gel filtration from the crude extracts of Alcaligenes denitrificans subsp. xylosoxydans MI-4. The enzyme was composed of a single polypeptide of about 51,000. The enzyme catalyzed hydrolysis of N-acyl-derivatives of neutral d-amino acids. Optimal pH and temperature were 7.8 and 50°C. The apparent Km and the Vmax for N-acetyl-d-phenylalanine were 14.1 mM and 1331 units/mg protein, respectively. The activity of the enzyme was inhibited by N-acetyl-d-valine (Ki=2.15 mM) and N-acetyl-d-alloisoleucine (Ki=1.47 mM), but not by its products (i.e., amino acids and acetate). The enzyme also had dipeptidase activity. Activation by metal ions was not observed.
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