Isolation of conglutin δ, a sulphur-rich protein from the seeds of Lupinus angustifolius L.

Although a 2S globulin class has been observed in salt extracts from seeds of several lupin species, there have been conflicting reports regarding the importance of this class in Lupinus angustifolius. Conglutin δ, a major sulphur-rich protein extracted from mature seeds of L. angustifolius cv. Uniwhite, was separated by gel-filtration into two oligomeric forms. The sedimentation coefficients of conglutin δ₁ (20%) and conglutin δ₂ (80%), were 3.2S and 2.0S respectively. The amino acid compositions of both oligomeric forms of conglutin δ were identical and similar to the compositions published for the 2S globulins in other lupin species. Because of the low level of tyrosine and the absence of tryptophan, conglutins δ₁ and δ₂ showed little absorbance at 280nm (E^1%/1 cm^?23). They were characterised by unusually high levels of glutamic acid and 1/2 cysteine (38.5 and 8.5 residues percent respectively) while methionine was absent. Gradient SDS-PAGE showed that conglutins δ₁ and δ₂ were homogeneous single-subunit species. On reduction, with or without S-carboxymethylation, both the conglutin δ₁ and δ₂ subunits yielded similar pairs of large and small polypeptide chains. Since conglutin δ rarely resolves from conglutin a during electrophoresis on cellulose acetate membranes in phosphate buffer at neutral pH, this method is not as useful for screening lupin cultivars as has been claimed previously.