title: Calcium binding constituents of the organic shell matrix from the freshwater snail Biomphalaria glabrata.
abstract: The Ca2+ binding of an EDTA-free water-soluble (SM) and -insoluble (IM) organic matrix of the freshwater snail Biomphalaria glabrata was investigated, using a 45Ca2+ autoradiography after SDS-electrophoretical separation and a calcium binding assay. Electrophoresis of the SM showed a considerable amount of Alcian blue and Stains all positive material, regarded as glycosaminoglycans (GAGs) or proteoglycans (PGs). This part of the SM was slightly positive after 45Ca2+ autoradiography at pH 6.8. The Ca2+ binding increased, raising the pH to 7.4 and 8.0 and was especially strong when simulating the real conditions of the extrapallial space with a carbonate buffer of pH 7.4. The Ca2+ binding assay of the IM showed the same pH-dependency that was observed in the SM. The titration of the IM with Ca2+ at pH 8.0 lead to a dissociation constant of 7.5 x 10(-5) M. While Mg2+ displaced 45Ca2+ in the same way as nonradioactive Ca2+, an approximately 400-fold amount of Na+ was necessary to reduce the binding of 45Ca2+ to 50%. The Ca2+ binding of the organic matrix from the B. glabrata shell appears to be a process of low specificity, medium affinity and high pH-dependency. Apparently, acidic carbohydrate-rich PGs are the only calcium binding constituents of the organic shell matrix.
authors.affiliation: Department of Zoology, University of Hamburg, Germany. marxen@zoologie.uni-hamburg.de
authors.forename: J C
authors.initials: JC
authors.lastname: Marxen
authors.forename: W
authors.initials: W
authors.lastname: Becker
mesh_terms: D000818:Animals; D001345:Autoradiography; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D006025:Glycosaminoglycans / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D011485:Protein Binding; D011509:Proteoglycans / Q000737:chemistry / Q000378:metabolism; D012908:Snails / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D006025:Glycosaminoglycans; D011509:Proteoglycans; D002118:Calcium