AN ELECTROPHORETIC INVESTIGATION OF GROUNDNUT PROTEINS: THE STRUCTURE OF ARACHINS A AND B

Abstract

The proteins of groundnut cotyledons were fractionated and analyzed by DEAE-Sephadex chromatography and acrylamide-gel electrophoresis. Seventeen components were detected. A new method is described for the preparation of arachin, using calcium precipitation. The product contains at least 99% of arachin. The theory of acrylamide-gel electrophoresis is developed and applied to the arachin system to predict the molecular weight of 1 subunit of arachin. A variant of arachin, arachin B, was discovered. Of 81 seeds, 27 contained only arachin B, 53 contained both arachin A and B, and 1 contained arachin A only. This is almost certainly a polymorphism of arachin; and is the 1st example of polymorphism to be reported in plant proteins. A combination of controlled denaturation, electrophoretic analysis, ultracentrifuge, and Sephadex filtration data showed that arachin A contains 4 different kinds of peptide chains ([alpha], [beta], [gamma], and [delta]). Arachin B contains only [beta], [gamma], and [delta] chains. The most probable structure for arachin B, mol.wt. 330,000 form, is 8 [beta], 2 [gamma], and 2[delta] chains, and for arachin A, 4[alpha], 4[beta], 2[gamma], and 2[delta] chains. Arachin without p chains was not found. The [alpha] and [beta] chains have nol. wts. of about 35,000, and [gamma] and [delta] chains of about 10,000. Three N-terminal groups were found: the [alpha] and [beta] chains both terminate in glycine; the [gamma] and [delta] chains terminate in isoleucine and glutamic acid. Arachin contains no carbohydrate. Disul-fide bonds are not important in arachin: there are none between the [alpha], [beta], [gamma], and [delta] chains. The amino acid compositions of arachins A and B are very similar. Glutamic acid and aspartic acid residues are exceptionally frequent.