Saracin: a lectin from Saraca indica seed integument recognizes complex carbohydrates.

A lectin isolated from Saraca indica seed integument was purified by affinity chromatography on porcine thyroglobulin Sepharose followed by Sephadex G-50 and shown to be homogeneous by PAGE. It showed a single band on SDS-PAGE in the absence and presence of 2-mercaptoethanol corresponding to a M(r) of congruent to 12,000, thus indicating it to be a monomer. The lectin agglutinated erythrocytes of human A, B, O and AB blood group, animal erythrocytes as well as Ehrlich ascites cells. It is a thermostable glycoprotein containing 11.6% carbohydrates and large proportions of acidic amino acids. In haemagglutination-inhibition assays, among the tested glycoproteins, porcine thyroglobulin having the NeuAc alpha (2-6)/(2-3)D-Gal beta (1-4)D-GlcNAc sequence was found to be the most potent; however, its asialo counterpart was non-inhibitory. The lectin is present solely in the seed integument even in the immature stage. During maturation of the seed the lectin activity declined and was completely absent when totally matured and dried. Studies in vitro showed that on incubation at 37 degrees the seed gradually lost its lectin activity which was completely absent after 62 days with 88.5% loss of water. Similar studies on scraped seed integument revealed that the lectin activity was lost in 22 days with 87.5% dehydration.