Primary structure of 2S albumin from seeds of Lupinus albus

The 2S albumin from the seeds of white lupin (Lupinus albus L.) was purified by ammonium sulfate precipitation and ultrafiltration followed by anion-exchange and reversed-phase HPLC. The complete amino acid sequences of the large and the dominating small subunit were determined by automated Edman degradation of the reduced and S-pyridylethylated polypeptides and of their enzymatic fragments. The small subunit of the 2S albumin (a) consists of 37 amino acid residues resulting in a molecular mass M(r) of 4407. The large subunit (b) contains 75 amino acid residues (M(r) = 8827). The two polypeptide chains are linked by two interchain disulfide bonds (Cys(a8)-Cys(b24) and Cys(a20)-Cys(b13) or, more probably, Cys(a20)-Cys(b12)). In addition, the large polypeptide contains two intrachain disulfide bridges (Cys(b26)-Cys(b68) and Cys(b12)-Cys(b60) or, more probably, Cys(b13)-Cys(b60)) and one free sulfhydryl group (Cys(b40)). A high degree of homology (88%) exists between the primary structure of the 2S albumin from L. albus and that of a comparable 2S protein from L. angustifolius, designated conglutin delta.