A. P. Wheeler

Evaluation of calcium binding by molluscan shell organic matrix and its relevance to biomineralization

Abstract 1. 1. EDTA used to dissolve mollusc shells associates with soluble matrix (SM) material and persists in SM preparations despite exhaustive conventional dialysis. 2. 2. EDTA-free oyster or clam SM material binds little calcium at physiological ionic strength. 3. 3. It is concluded that residual EDTA or failure to determine binding in physiological media may lead to binding artefacts and that hypotheses which rely on SM calcium binding to explain initiation of biomineral formation need to be re-evaluated. 4. 4. It is hypothesized that crystal binding, rather than calcium binding, by SM is responsible for initiation of biomineral formation.

A Systematic Approach to Some Fundamental Questions of Carbonate Calcification

Our studies of the physiology of carbonate calcification have been organized to address five general questions about the process: 1)what are the sources and forms of dissolved inorganic carbon, 2)what is the role of active transport, 3)what is the role of carbonic anhydrase, 4)how is pH regulated, and 5)what is the role of organic matrix? The studies feature several organisms including coccolithophorids, oysters, freshwater clams, and sea urchin embryos. The results are summarized here and current interpretations presented.

Large Scale Thermally Synthesized Polyaspartate as a Biodegradable Substitute in Polymer Applications

Polyanionic proteins isolated from biominerals serve as models for the development of biodegradable surface-reactive commercial polymers. A simple model for the natural polyanions is polyaspartic acid. This polymer may be made on a large scale using thermal polymerization of dry aspartic acid. The immediate result of the reaction is polysuccinimide which is hydrolyzed with base to form the polypeptide. The overall process yields up to 99% conversion of aspartic acid to polyaspartate. The thermal polyaspartate (TPA) is a copolymer having 70% of the amide bonds formed from β-carboxyl groups and 30% from α-carboxyl groups. TPA is as effective as the commercial polyanion polyacrylate in mineral dispersion and growth inhibition assays. Biodegradation of the TPA has been established using standard BOD and CO 2 evolution assays. In contrast, polyacrylates appear to be non-degradable. Modifications of the TPA have been made by reacting the succinimide with nucleophiles. Crosslinking of the polymer has been achieved, a process which results in absorbent gels. Because TPA can be produced in large scale, has similar activity to polyacrylate and is biodegradable, it seems a likely candidate for use in numerous applications in which non-degradable polyanions are employed. These applications include use as detergent additives, water treatment chemicals, dispersants for the paint and paper industry and as superabsorbents in health and sanitary products.

Subcellular localization and characterization of HCO3−-ATPase from the mantle of the freshwater clam, Anodonta cataracta

1. HCO3(-)-stimulated ATPase activity was demonstrated in mantle tissue of the freshwater clam, Anodonta cataracta. 2. Calcium (1 mM) slightly inhibited and SCN- completely inhibited HCO3(-)-stimulation of the enzyme. 3. ATPase activity had a Km of 6.8 mM for HCO3(-)-activation and was inhibited at HCO3(-)-concentrations greater than 20 mM. 4. Subcellular fractionation studies revealed the presence of both a mitochondrial and a non-mitochondrial HCO3(-)-ATPase.