D-Galactose binding lectins from the tunicate Ascidia malaca: Subunit characterization and hemocyte surface distribution

D-galactose specific lectins purified from Ascidia malaca serum contain a major protein component with an apparent molecular weight of about 58,000 daltons, which moves more rapidly under non-reducing conditions. Intramolecular disulfide linkages can explain this behaviour, suggesting a compact protein structure. Membrane lectins have been demonstrated on the surface of about 34% hemocytes by immunofluorescent methods using a rabbit antiserum against the isolated serum lectins. Small, medium and large hemocytes can be positive, as also shown by binding on Sepharose spherules or by rosette formation with sheep and rabbit erythrocytes. Binding is inhibited by the same sugars specific for the serum lectins. Finally, antibodies to the serum lectins specifically agglutinate the hemocytes. This evidence supports the hypothesis that a lectin with the same specificity and certain structural similarities can be found free in the serum and present on hemocyte surfaces. © 1988.