Identification of the Acidic and Basic Subunit Complexes of Glycinin (1)
major polypeptides present in each of the two major subunit groups were purified and identified unambiguously on the basis of their NH2-terminal and partial internal amino acid sequences. Six acidic (A1a, A1b, A2, A3, A4,and F2(2)) and five basic (B1a,B1b,B2,B3,and B4) polypeptides having homologous but distinct sequences were found. At least some of the acidic and basic subunits are linked with one another via disulfide bonds to form acidic-basic polypeptide complexes (AB- complexes).
Glycinin-Nonreduced glycinin was purified using the procedure of Moreira et al., except that sulfhydryl-reducing agents were removed from the buffers. Sodium dodecyl sulfate-polyacrylamide electrophoresis of purified unreduced glycinin yielded a major band at M, = 57,000 and a minor one at about 30,000. Exposure of the unreduced glycinin to 2-mercaptoethanol prior to electrophoresis resulted in breakdown of the complexes into the component acidic (Mr = 37,000-42,000) and basic (Mr = 20,000) subunits.
Translating mRNA purified from developing seeds results in the synthesis of a M, = 60,000 polypeptide which can be selectively immunoprecipitated by anti glycinin-IgG. There is an 8-fold difference between the complexes having the highest and lowest methionine content.
More importantly, the high methionine acidic and basic subunits pair together, while those low in methionine are also paired.
