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 δ 1 (20%) and conglutin δ 2 (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 δ 1 and δ 2 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 δ 1 and δ 2 were homogeneous single‐subunit species. On reduction, with or without S‐carboxymethylation, both the conglutin δ 1 and δ 2 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.