Natural shedding of carbohydrate-containing macromolecules from cell surfaces

The turnover of the chick embryo cell surface was examined, using as markers the cell surface charge and the receptor site of wheat germ agglutinin. The rates observed (1-8 h) were similar to those reported for other surface markers and other cell types. Labelling the cell surface with glucosamine resulted in labelled macromolecules appearing in the medium. When these were co-chromatographed on DEAE cellulose columns together with the labelled surface constituents released from the cells by trypsin treatment, the profiles obtained were strikingly similar. It was also found that the material shed by mouse cells carries H-2 histocompatibility specificities. It is proposed that cell surface constituents are released into the surrounding medium under normal physiological conditions as part of the surface membrane turnover, and various aspects of this shedding are discussed.