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  • Title: Purification and characterization of paralytic shellfish toxin transforming enzyme from Mactra chinensis.
    Author: Lin HP, Cho Y, Yashiro H, Yamada T, Oshima Y.
    Journal: Toxicon; 2004 Nov; 44(6):657-68. PubMed ID: 15501292.
    Abstract:
    A carbamoylase, which catalyzes hydrolysis of the carbamoyl (or N-sulfocarbamoyl) moiety of paralytic shellfish toxins, was purified from the digestive glands of the Japanese clam Mactra chinensis. Using five steps of column chromatography, 290 microg of Carbamoylase I showing homogeneity on SDS-PAGE was obtained. Carbamoylase I was revealed to be a glycoprotein, having estimated molecular weight of 190 kDa. Observation of single band equivalent to 94 kDa on SDS-PAGE under reducing conditions suggested it to be a homodimer. The optimal temperature and pH were 20 degrees C and 7.0. Carbamoylase I did not require a divalent cation and its activity was inhibited by the serine proteinase inhibitors, benzenesulfonyl fluoride and 4-(2-aminoethyl)-benzenesulfonyl fluoride. Carbamoylase I hydrolyzed both carbamate and N-sulfocarbamate toxins. The presence or absence of a hydroxyl moiety at the N-1 position of the substrate toxins did not significantly alter the reaction rate, but the stereochemistry of sulfate esters at C-11 greatly affected it. The K(m) was 3.02 microM for saxitoxin as a substrate. Nineteen amino acids of the N-terminal sequence were identified by the Edman method. MALDI-TOF-MS/MS spectra of (18)O-labeled tryptic peptides indicated the possible internal amino acid sequences of five peptides.
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