Occurrence of saxitoxin and related toxins in Palauan bivalves

Purification and characterization of paralytic shellfish toxin transforming enzyme from Mactra chinensis

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.

Nonprotein neurotoxins

Nonprotein neurotoxins are continuing to play a major role as molecular probes in studying nervous processes. They also have clinical importance as some of them, such as saxitoxin and its analogues, are the source of public health problems, or have potential use in therapy. This review covers clinical, biological, pharmacological, and chemical aspects of certain nonprotein neurotoxins, with emphasis on three well-known ones: tetrodotoxin, saxitoxin, and batrachotoxin. The distribution of the toxins is discussed as well as their symptomatology, treatment of affected patients, and effects of their structures on their physiological activity. With so many outstanding problems remaining in neuropharmacology, the study of nonprotein neurotoxins thrives as a fertile area of research.