Identification of lectin isoforms in juvenile freshwater prawns Macrobrachium rosenbergii (DeMan, 1879)

From the serum of juvenile freshwater prawns, we isolated by affinity chrom atography on glutaraldehyde-fixed rat erythrocytes stroma, immobilized in S ephadex G-25, a sialic acid specific lectin of 9.6 kDa per subunit. Compara tive analysis against adult organisms purified lectin, by chromatofocusing, showed that the lectin from juvenile specimens is composed by four main is oforms with a pl of 4.2, 4.6, 5.1, and 5.6, whereas the lectin from adults is eluted at pH 4.2. The amino acid composition of the lectin obtained from adult and juvenile stages suggest identity, but the compositions are not i dentical since a higher content of carbohydrates was found in the lectin fr om younger organisms. The freshwater prawn lectin showed specificity toward N-acetylated amino sugar residues such as GlcNAc, GalNAc, Neu5Ac and Neu5, 9Ac; but in juvenile organisms the lectin showed three times less hemagglut inating activity than the lectin from adults. Both lectins agglutinated rat , rabbit and chicken erythrocytes, indicating that Neu5,9Ac in specific O-g lycosydically linked glycans seems to be relevant for the interaction of M. rosenbergii lectins with their specific cellular receptor. Our results sug gest that the physicochemical characteristics of the lectin from the freshw ater prawn are regulated through maturation.