Abstract
1. The proteins of the groundnut cotyledon have been fractionated and analysed by DEAE-Sephadex chromatography and acrylamide-gel electrophoresis. Seventeen components were detected. 2. A new method is described for the preparation of arachin, using calcium precipitation. The product contains at least 99% of arachin. 3. The theory of acrylamide-gel electrophoresis is developed and applied to the arachin system to predict the molecular weight of one sub-unit of arachin. 4. A variant form of arachin, arachin B, has been discovered. Of 81 nuts, 27 contained only arachin B, 53 contained both arachin A and B, and one contained arachin A only. This is almost certainly a polymorphism of arachin; this is the first example of polymorphism to be reported in plant proteins. 5. A combination of controlled denaturation, electrophoretic analysis, ultracentrifuge and Sephadex filtration data has shown that arachin A contains four different kinds of peptide chains (alpha, beta, gamma and delta). Arachin B contains only beta, gamma and delta chains. 6. The most probable structure for arachin B, mol.wt. 330000 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 beta chains was not found. 7. The alpha and beta chains have mol.wts. of about 35000 and the gamma and delta chains of about 10000. 8. 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. 9. Arachin contains no carbohydrate. 10. Disulphide bonds are not important in arachin: there are none between the alpha, beta, gamma and delta chains. 11. The amino acid compositions of arachins A and B are very similar. Glutamic acid and aspartic acid residues are exceptionally frequent.