Isolation and characterization of galactose-binding proteins from new-born mice

Two galactose-binding proteins were purified from the soluble extracts of new-born mice by affinity chromatography using a column of lactamyl-Sepharose. The molecular masses of their subunits were 15 (galactose-binding protein 15K) and 16 (galactose-binding protein 16K) kDa, and the isoelectric points were 5.3 and 6.8, respectively. These galactose-binding proteins agglutinated formaldehyde-fixed trypsinized rabbit erythrocytes. Hemagglutinating activity was inhibited by galactose-containing saccharides and glycopeptides. N-Acetyllactosamine and asialo-glycopeptides having N-acetyllactosamine at non-reducing termini were found to be the most effective inhibitors so far examined. These results suggest that galactose-binding proteins can recognize lactosaminoglycans on erythrocyte surfaces. The elution patterns of gel filtration by high performance liquid chromatography showed galactose-binding protein 15K to form dimers of identical subunits, galactose-binding protein 16K to be monomeric, and neither to interact with each other under the conditions employed. The results obtained by immuno-blotting with antisera raised against purified galactose-binding proteins and amino acid analyses indicate that galactose-binding proteins 15K and 16K are not identical molecules. The distribution of galactose-binding protein 15K on frozen sections of new-born mice was surveyed by indirect immunofluorescence staining. Galactose-binding protein 15K was found widely distributed on many tissues, and distinct staining was observed in the liver and epidermis but not in the brain of unfixed samples.