Embryonic cell aggregation: kinetics and specificity of binding of enhancing factors

A new assay for tissue-type-specific adhesive macromolecules is described. This assay measures the binding to whole cells of radioactive macromolecules in aggregation-enhancing supernatants. We show for two tissue types, embryonic chick neural retina and cerebrum, that binding is tissue-type specific. Specific binding can be distinguished from nonspecific binding by its sensitivity to displacement with horse serum and by the kinetics of binding. Specific binding appears to be a cooperative phenomenon.