The turnover of a tissue specific cell surface ligand which inhibits lectin induced capping.

Ten-day-old embryonic chick neural retina release into the environment glycoprotein ligands which bind to homologous cells, inhibiting the lectin-induced redistribution of cell surface receptors. Material with identical activity is released from trypsin-dissociated neural retina cells that are allowed to repair in culture for 2 h and are then transferred to fresh medium. Release of ligand is inhibited by cytosine arabinoside, hydroxyurea, UDP, and EDTA, and is potentiated by MnCl2. These data suggest that a glycosyltransferase reaction plays a critical role in the turnover of the cell surface ligand. Reactivation of enzymatically deglycosylated ligand solutions by intact cells provides further support for this hypothesis. Release of ligand is also accompanied by a loss of the agglutinability of the cells by a tissue-specific component which accumulates in monolayer conditioned medium. Conditions which inhibit release maintain maximal agglutinability suggesting similar mechanisms mediate both processes.