Sulfomucopolysaccharide or acid mucoprotein with sulfate group is detected in mantle mucus of some bivalves4-7), and is considered to act as a calcium carrier and provide calcium concentration high enough for the growth of shell minerals at the site of mineralization4). Histochemical and biochemical studies have suggested that the inner and outer mucus of the mantle of Pinctada fucata show metachromasia on staining with toluidine blue and are very similar to each other in their amino acid compositions1). If the acid mucous substances play the above-mentioned functional role in the calcium metabolism of molluscs, the mucus does not always form a shell. To answer this quesion, biochemical analysis of the acid polysaccharide was made on the inner and outer mucus of the mantle of Pinctada fucata and Chlamys nobilis.
Inner mucus adhered on the inner surface of the mantle and outer mucus secreted between the mantle and shell were collected with an injector. In each case the dry mucus obtained by addition of ethyl alcohol was digested with “pronase” at pH 8.0 and 50°C for 72 hours and subsequently with trypsin at pH 7.5 and 37°C for 72 hours. Acid polysaccharide was then separated by the cetyl pyridinium chloride treatment and analysed as described in the preceding paper2).
The amount and chemical composition of fraction A containing acid mucopolysaccharide are shown in Tables 1 and 2. The fraction contains a relatively large amount of sulfuric ester and a little amount of protein, but not chondroitine sulfate, as shown by paper electrophoresis. Galactosamine, glucosamine, galactose and glucose are detected in fraction A of both the inner and outer mantle mucus of Pinctada fucata by paper chromatography (Table 3). The fraction seems to be composed of sulfomucopolysaccharide or sulfated polysaccharide-protein complex.
From these results, it may be concluded that the presence of the acid mucous substance with sulfate group is necessary to induce shell mineralization though it does not always induce it.