Interaction of monomeric and oligomeric soybean agglutinins with pig lymphocytes and plasma membranes.

The pig lymphocyte surface contains two distinct receptor classes for monomeric (nonmitogen) and oligomeric (mitogen) soybean agglutinins. The major class (70-80%) for which both forms compete effectively binds them with a similar weak avidity in a non-cooperative monovalent reaction. This class appears to be one or more plasma membrane glycolipids and not involved in the mitogenic process. The minor class (20-30%) binds the monomer weakly and non-cooperatively. It binds the oligomers strongly via positively cooperative interactions involving mobile surface molecules in a metabolically energy-independent clustering process. The minor class appears to be one or more of seven plasma-membrane glycopolypeptides. The monomer does not compete effectively for this class nor does it specifically inhibit the mitogenicity of the oligomers, suggesting that receptors involved in the mitogenic process fall into the minor class and are likely to be glycopolypeptides.