Comparison of the Maclura pomifera lectin-binding glycoprotein in late fetal and adult rat lung

The lectin, Maclura pomifera agglutinin (MPA), binds to alphagalactose residues of glycoproteins on the apical surface of type II alveolar cells. It has recently been shown to bind to macrophages. We isolated the cell surface glycoprotein, which binds the MPA lectin, from fetal and adult rat whole lung to determine if changes in this glycoprotein occur during development from fetal to adult life. The glycoprotein was purified from whole lung cell membranes by lectin affinity chromatography that resulted in 10⁵-fold enrichment. The MPA binding glycoproteins from both fetal and adult lung had the same apparent molecular weight of 170 kD as determined by sodium dodecylsulfate-polyacrylamide gel electrophoresis. Amino acid analysis revealed similar composition of the fetal and adult proteins. Two-dimensional peptide maps of the 170 kD proteins isolated from fetal and adult lung were also similar. These data indicate that the glycoprotein that binds MPA to lung cell membranes does not change during this stage of development. Our method for the isolation of this glycoprotein can be used for the generation of antibodies or other molecular probes for further study of this protein.