BENTHIC MUCILAGINOUS AGGREGATES - BIOCHEMICAL-CHARACTERIZATION AND LIGAND-BINDING PROPERTIES

The biochemical composition of benthic mucilaginous aggregates collect ed from the south-western coastal waters of Sardinia in the Mediterran ean Sea was analysed. Acidic glycoproteins surrounding the included mi croorganisms, mainly diatoms, were found to be the predominant fractio n. The aggregates, diluted and finely dispersed by ultrasonic treatmen t, bound with ammoniated ruthenium oxychloride (ruthenium red), a spec ific ligand for the acidic glycoproteins. When concentrated crude aggr egates were used ruthenium red was bound both chemically and by physic al entrapment. The data were consistent with the Langmuir ligand binni ng isotherm. The extent of physical adsorption displayed a clear pH de pendence. Physical adsorption was predominant at acidic pH, suggesting that the stabilization of the supramolecular structure of the aggrega tes also depends on the degree of protonation of the acidic glycoresid ues. A structural model of the aggregates is proposed, where the mucus matrix containing acidic binding sites acts as an intercellular glue, providing a molecular sieve-like filtering capacity to the aggregates dispersed in seawater.