Studies on phytohemagglutinins. XXII. Isolation and characterization of a lymphocyte receptor for concanavalin A

Isolation and chemical characterization of a highly purified phytomitogen from Phaseolus coccineus seeds

An effective lymphocyte mitogen with a low erythroagglutinating ability was isolated from the seeds of Phaseolus coccineus L. by ammonium sulphate precipitation and repeated ion-exchange chromatography on modified Sephadex. The mitogen stimulated lymphocytes at concentrations as low as 0.25 microgram/ml, the optimum concentration being in the range of 2.5-5.0 microgram/ml. This stimulating effect was completely inhibited by 5 mg/ml methyl alpha-D-mannopyranoside. Column gel filtration, disc electrophoresis on polyaceylamide gel in an alkaline medium and in the presence of sodium dodecylsulphate and the finding of a single N-terminal amino acid (alanine) showed the phytomitogen to be homogenous. Disc electrophoresis in an acid medium revealed the presence of two or three bands which are assumed to be due to aggregates of the mitogen. The minimum molecular weight, as derived from sodium dodecylsulphate electrophoresis on polyacrylamide, was 35000. The mitogen is a glycoprotein containing 10% neutral sugars and 1.3% amino sugars (glucosamine). The amino acid composition of the isolated phytomitogen is presented.

Studies on phytohemagglutinins. XXVII. A study of the pea lectin binding site

Under defined mild conditions the reaction of the pea lectin with 2-nitrophenylsulfenyl chloride results in sulfenylation of only 2 of the 10 tryptophan residues of the lectin molecule with simultaneous loss of biological activity. Both sulfenylated tryptophan residues belong to the two heavy subunits of the lectin. Enzymic hydrolysis and separation of the tryptic peptides yields only one homogeneous yellow peptide containing the modified tryptophan residue. The isolated peptide has the following sequence (NPS, nitrophenylsulfenyl): HAsp-Val-Val-Pro-Glu-(2-NPS-Trp)-Val-ArgOH. The octapeptide is either directly a part of the pea lectin binding site or it plays an important role in maintaining the tertiary structure of the binding site. According to the amino acid composition and amino acid sequence, the octapeptide isolated from the pea lectin is almost identical with that part of the peptide chain of concanavalin A near to which the location of the sugar binding site is supposed to be.