Abstract
Cell surface glycoconjugate receptors for wheat germ aggluti-nin, Ricinus communis agglutinin, concanavalin A and soybean agglutinin on two strains of myxoamoebae of Physarum polycephalum with fluorescein isothiocynate-labelled lectins were observed microscopically, but no receptors for Dolichos biflorus agglutinin, Ulex europeus agglutinin-I and Arachis hypogaea agglutinin were found. These results suggest that the myxoamoebae have cell surface glycoproteins with N-glycosidically linked hetero-saccharide chains, but not oligosaccharides with blood group A and H determinants. The number of lectin receptor sites and their affinity constants for lectins were obtained for the myxoamoebae and microplasmodia of P. polycephalum from binding assays with 125I-lectins. The densities of these lectin receptors and the magni-tudes of the affinity constants were similar to those of mammalian cells. Neuraminidase treatment of the myxoamoebae and microplasmodia induced neither a decrease in WGA receptors nor an increase in RCA receptors. These results are strong evidence that sialyl residues are absent in glyco-conjugates on the surface of the myxoamoebae and microplasmodia of P. polycephalum.
