COMPARATIVE CROSS-LINKING ACTIVITIES OF LACTOSE-SPECIFIC PLANT AND ANIMAL LECTINS AND A NATURAL LACTOSE-BINDING IMMUNOGLOBULIN-G FRACTION FROM HUMAN SERUM WITH ASIALOFETUIN

Plant and animal lectins bind and cross-link certain multiantennary ol igosaccharides, glycopeptides, and glycoproteins, This can lead to the formation of homogeneous crosslinked complexes, which may differ in t heir stoichiometry depending on the nature of the sugar receptor invol ved, As a precisely defined ligand, we have employed bovine asialofetu in (ASF), a glycoprotein that possesses three asparagine-linked triant ennary complex carbohydrate chains with terminal LacNAc residues, In t he present study, we have compared the carbohydrate cross-linking prop erties of two Lac-specific plant lectins, an animal lectin and a natur ally occurring Lac-binding polyclonal immunoglobulin G subfraction fro m human serum with the ligand, Quantitative precipitation studies of t he Lac-specific plant lectins, Viscum album agglutinin and Ricinus com munis agglutinin, and the Lac-specific 16 kDa dimeric galectin from ch icken liver demonstrate that these lectins form specific, stoichiometr ic cross-linked complexes with ASF, At low concentrations of ASF, 1:9 ASF/lectin (monomer) complexes formed with both plant lectins and the chicken lectin, With increasing concentrations of ASF, 1:3 ASF/lectin (monomer) complexes formed with the lectins irrespective of their sour ce or size, The naturally occurring polyclonal antibodies, however, re vealed a different cross-linking behavior. They show the formation of 1:3 ASF/antibody (per Fab moiety) cross-linked complexes at all concen trations of ASF, These studies demonstrate that Lac-specific plant and animal lectins as well as the Lac-binding immunoglobulin subfraction form specific stoichiometric cross-linked complexes with ASF, These re sults are discussed in terms of the structure-function properties of m ultivalent lectins and antibodies.