THE IMPLICATION OF CARBONIC ANHYDRASE IN THE PHYSIOLOGICAL MECHANISM OF PENETRATION OF CARBONATE SUBSTRATA BY THE MARINE BURROWING SPONGECLIONA CELATA(DEMOSPONGIAE)

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Abstract
The marine burrowing sponge, C. celata Grant, excavates anastomosing or dendritic galleries in calcareous substrates. The physiological capability of the sponge to produce an acidic etching agent or otherwise alter the ion concentration product and affect the dissolution of CaCO3 is studied. Using a modified electrometric assay, with 0.025 M trisaminomethane buffer, carbonic anhydrase activity was demonstrated in extracts of clionid tissues. Acetazolamide-induced inhibition (10-4 M) of the sponges carbonic anhydrase reduced the ability of the sponge to excavate Mercenaria mercenaria valves by a factor of 20. Similar concentrations of acetazolamide did not provoke papillary contraction or reduce basal metabolic rate. There was a positive correlation between the excavating activity of the sponge and the level of carbonic anhydrase in the sponge tissues. The primary mechanism for the dissolution of CaCO3 by C. celata involves a shift in the carbonate solubility product in the microenvironment of the etching cells mediated through activity of the enzyme carbonic anhydrase. Production of H+ ions resulting from the hydration of CO2 within the etching cells is a logical mechanism by which this could be accomplished. This production of H+ ions may provide pH optimization for the enzymatic dissolution of the organic matrix (conchiolin) of the molluscan shell.