Asialofetuin (ASF) coupled to Sepharose has been used to isolate a Mr 30,000 protein from Triton X-100 extracts of the baby hamster kidney cell line BHK21 C13. Binding to ASF-Sepharose was specific for terminal beta-galactosyl residues. The lectin requires detergent for optimal solubilization and binding is independent of Ca2+ or reducing reagents. The lectin was labelled in a lactoperoxidase-catalysed iodination of intact BHK21 C13 cells, suggesting that it is associated with the cell surface. Antibodies to the lectin identify in Western blotting cross-reactive components in established cell lines of kidney (MDCK, NRK) and non-kidney (L, CHO, 3T3) origin. In young adult hamsters, the lectin is expressed in colon and duodenum and in lesser amounts in ileum, stomach, lung, liver and testes but is absent in kidney. The lectin is expressed in late embryonic and newborn hamster kidney but expression declines during 14 days after birth. Immunofluorescent staining of cryostat sections of newborn hamster kidney and intestine show that the lectin is expressed at apical epithelial surfaces. The presence of the lectin at the luminal surface of kidney tubules suggests a tubular origin for the BHK21 C13 cell line. Possible functions of the Mr 30,000 lectin in kidney development are discussed.

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