Precursors of storage proteins in Lupinus angustifolius

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Abstract
The proteins that are synthesized during differentiation and development in the cotyledons of L. angustifolius L. were characterized both in situ and after purification. The proteins present in situ were separated by sodium dodecyl sulfate/polyacrylamide-gel electrophoresis and subjected to Western-blot analysis to identify immunologically related polypeptides. The major storage proteins of the lupine, conglutins .alpha. and .beta., were both present in juvenile tissue only as higher MW precursors. For conglutin .beta., a family of at least 3 polypeptides of MW 66,000-72,000 accumulated during the earliest phases of protein synthesis in the developing cotyledon (20-28 days after flowering). Later in development each of these polypeptides disappeared and there was the concurrent appearance in the cotyledon of the lower-MW fragments characteristic of mature conglutin .beta.. For conglutin .alpha., an equivalent family of precursor polypeptides of MW 60,000-83,000 was detected. Multiple internal sites for proteolytic cleavage of all these precursors appeared to be present. Processing of the precursors was sufficiently slow to allow them to accumulate to > 50% of total soluble protein in juvenile tissue. The precursors were purified by column chromatography under non-dissociating conditions and shown by ultracentrifugation to be multimeric proteins with MW values in the range 150,000-200,000.

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