Identification, Purification and Properties of the Precursor of Conglutin β, The 7S Storage Globulin of Lupinus albus L. Seeds

Lupinus albus L. developing cotyledons 35 d after flowering contained a major polypeptide of-average Mr 64000, immunologically related to conglutin β, the 7S storage globulin of this seed. This polypeptide decreased during seed maturation, without completely disappearing in the mature seed. This drop was accompanied by the formation of polypeptide fragments typical of the mature conglutin β. The 64000 polypeptide has been identified as the precursor polypeptide of conglutin β. Undenatured conglutin β precursor, purified by ion exchange chromatography and size exclusion chromatography, showed surface and association properties identical to the mature conglutin β molecule. The precursor oligomer, of Mr 190000, consisted of an association of three 64000 subunits. They strongly reacted with concanavalin A indicating the presence of covalently linked carbohydrate. Tryptic treatment of the undenatured conglutin β precursor led to the accumulation of a relatively stable 59000 polypeptide which was cleaved later on and produced three large polypeptide fragments differing from the mature conglutin β polypeptides.