Extensive homology between the subunits of the phytohemagglutinin mitogenic proteins derived from Phaseolus vulgaris.
The phytohemagglutinin mitogenic proteins derived from Phaseolus vulgaris comprise a class of five glycoproteins that are isomeric tetramers composed of varying proportions of two different subunits (L and R). Within the native tetramer, the L subunit is a potent leukoagglutinin and mitogen that lacks hemagglutinating properties, whereas the R subunit is a potent hemagglutinin with little or no mitogenic activity. The subunits have been isolated in homogeneous form by isoelectric focusing in 8 M urea. Previous work has shown that they have equal molecular weights and differ in amino-acid sequence from residues 1-7, but are identical in positions 8-24 [(1973) J. Exp. Med. 138, 939-951]. We now report amino-acid composition studies which reveal striking similarities between the subunits. Both lack methionine and cysteine. The twelfth residue in each subunit is a glycosylated asparagine, with the identical  carbohydrate composition in each. The last three residues of the subunits, as determined by carboxypeptidase A digestion, are identical. Tryptic peptide mapping of the succinylated phytohemagglutinin subunits reveals a high degree of similarity. We conclude that the substantial difference in biological properties among the tetrameric phytohemagglutinin mitogens is a result of relatively restricted differences in the primary structure of their constituent subunits.
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D002268:Carboxypeptidases; D037102:Lectins; D010446:Peptide Fragments / Q000032:analysis; D037121:Plant Lectins; D010944:Plants / Q000032:analysis; D014357:Trypsin
D000596:Amino Acids; D037102:Lectins; D010446:Peptide Fragments; D037121:Plant Lectins; D002268:Carboxypeptidases; D014357:Trypsin