Isolation, Purification and Characterization of the Seed Globulins of Lupinus angustifolius

Abstract

The three globulins of the seeds of L. angustifolius cv. Uniwhite may be satisfactorily resolved in 10 min by electrophoresis on cellulose acetate strips. These globulins, conglutins α, β and γ, vary markedly in their amino acid compositions, with conglutin Ω differing from conglutins α and β and most other legume storage proteins in its relatively high content of cystine and methionine and lower content of arginine and glutamic acid. When examined on sodium dodecyl sulphate-polyacrylamide gels, both in the absence and presence of β-mercaptoethanol, the three globulins were found to differ completely in the type of subunit proteins they contain and in the significance of intrachain disulphide bonding. Conglutin α was found to contain three or four types of non-covalently linked subunits with apparent molecular weights in the range 55 000-80 000, each of which may contain a disulphide-bonded moiety with a molecular weight near 20 000. Conglutin γ was found to contain disulphide-bonded chains of molecular weights 17 000 and 30 000, whereas the four major subunits of conglutin β, whose molecular weights lie in the range 20 000-60 000, were not covalently linked together. The latter globulin does not appear to be homogeneous, for it can be separated by fractional precipitation with ammonium sulphate into a series of fractions which differ markedly in the proportion of subunit types they contain.