Intact chicken embryo neural retina cells have been shown to catalyze the transfer of galactose-14C from uridine diphosphate galactose (UDP-galactose) to endogenous acceptors of high molecular weight as well as to exogenous acceptors. Four lines of evidence indicate that the galactosyltransferases catalyzing these reactions are at least partly located on the outside surface of the plasma membrane: (a) there is no evidence for appreciable uptake of sugar-nucleotides by vertebrate cells nor did unlabeled galactose, galactose 1-phosphate, or UDP-glucose interfere with the radioactivity incorporated during the reaction; (b) the cells remained essentially intact during the course of the reaction; (c) there was insufficient galactosyltransferase activity in the cell supernatants to account for the incorporation of galactose-14C into cell pellets; and (d) the intact cells could transfer galactose to acceptors of 106 daltons, and the product of this reaction was in the extracellular fluid. Appropriate galactosyl acceptors interfered with the adhesive specificity of neural retina cells; other compounds, which were not acceptors, had no effect. These results suggested that the transferase-acceptor complex may play a role in cellular recognition.

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