Phaseolus vulgaris agglutinin is the name ascribed to a family of lectins, each of which consists of four subunits. There are two different types of subunits. One appears to be involved primarily in red cell agglutination and has been designated the “E” subunit (for erythroagglutinin). The other type is involved in lymphocyte agglutination and mitogenic activity and has been termed the “L” subunit (for leucoagglutinin). These subunits combine to produce five isolectins.
One of these isolectins has four “E” subunits and is designated PHA-E. PHA-E possesses strong hemagglutinating activity but is a poor mitogen.