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The protein and glycoprotein content of four different neutral or acidic solvent extracts (0.5 M KCl, 10% EDTA, 0.1 N HCl, or 2% acetic acid) from the mineralized exoskeleton of a decapod crustacean, the Atlantic shore crab Carcinus maenas, were characterized by quantitative analysis of proteins, SDS-PAGE analysis, and probing with lectins on blots. The lectins used were Conconavalin A, Jacalin, soybean agglutinin, Maackia amurensis agglutinin II, and Sambucus nigra agglutinin. The results show that many proteins can be obtained from the crab cuticle without strong denaturants in the extraction medium. Many of the extracted cuticle proteins appeared to be glycosylated, bearing O-linked oligosaccharides and N-linked mannose-rich glycans. N-acetyl-galactosamine and N-acetylneuraminic acids were revealed, for the first time, as terminal residues on N-linked mannose-rich structures of crab cuticle glycoproteins. Sialylated glycoproteins might thus be involved in organic-mineral interactions in the calcified crab exoskeleton. The amount and variety of glycoproteins extracted with the acidic solvents are obviously different from those extracted with neutral solvents. HCl proved to be the best of the tested extraction solvents and a valuable alternative to EDTA.

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The biochemical composition of Daphnia magna Straus, the dominant planktonic crustacean of the waste stabilisation pond of Differdange (Grand-Duchy of Luxembourg), was quantitatively determined from October 1993 to July 1994. Over the sampling period, the average composition (mean ± S.D.) was 271 ± 64 mg proteins.g -1 dry weight (DW), 100 ± 28 mg lipids.g -1 (DW), 96 ± 58 fig carotenoids.g-1 (DW), 49 ± 14 mg chitin.g" 1 (DW) and 125 ± 78 mg ash.g" 1 (DW). The seasonal variations of the biochemical composition were related to several ecological variables (water temperature, dissolved oxygen concentration, pH, water transparency, chlorophyll a concentration and D. magna biomass). The chitin content was positively correlated to the water temperature as a result of the strong influence of this later variable on the moulting rate of the daphnids and, subsequently, on the chitin synthesis by these organisms. The carotenoid content was positively correlated to the water transparency as a result of their photoprotective role in daphnids. The fluctuations of the lipid, protein and ash levels in D. magna depended to the food availability. Despite a seasonal variation in the biochemical composition, D. magna appeared to have adequate lipid and protein levels to be used in aquaculture. Its carotenoid content is similar to fish meals used to color salmonid flesh and these organisms could be used for this purpose. The prospect of using D. magna for chitin extraction is worth considering with respect to its significant chitin content, especially if highly valuable applications are aimed.Analyse de la variation saisonnière de la composition biochimique de Daphnia magna Straus (Crustacea : Branchiopoda : Anomopoda) vivant dans un étang de lagunage aéré Mots-clés : Daphnia magna, lipides, protéines, caroténoïdes, chitine, composition biochimique, étang de lagunage, aquaculture. La composition biochimique de Daphnia magna Straus, le crustacé planctonique dominant dans l'étang de lagunage de Differdange (Grand-Duché de Luxembourg), a été déterminée quantitativement d'octobre 1993 à juillet 1994. Pendant cette période, la composition moyenne a été caractérisée par des teneurs s'élevant à (moyenne ± écart-type) 271 ± 64 mg protéines.g" 1 masse sèche (MS), 100 ± 28 mg lipids.g" 1 (MS), 96 ± 58 ug caroténoïdes.g" 1 (MS), 49 ± 14 mg chitine.g" 1 (MS) and 125 ± 78 mg cendres.g-1 (MS). Les variations saisonnières de la composition chimique des daphnies ont été mises en relation avec plusieurs variables écologiques (température de l'eau, concentration en oxygène dissous, pH, transparence de l'eau, concentration en chlorophylle a et biomasse de D. magna). La teneur en chitine s'est avérée positivement corrélée à la température de l'eau en raison de l'influence marquée de celle-ci sur le rythme de mue des daphnies et, par conséquent, sur la synthèse de chitine chez ces organismes. Le contenu en caroténoïdes s'est révélé positivement corrélé à la transparence de l'eau en raison du rôle de photoprotection de ces pigments. Les fluctuations des ...