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The G2 (A2BIa) glycinin subunit from soybean (Clycine mux L. Merr.) was purified and renatured to the homohexameric holoprotein. This protein along with purified P-conglycinin were subjected to limited proteolysis by trypsin. The generated polypeptide fragments were separated via SDS/PAGE and the amino acid sequence of the N-terminals was determined. Four cleavage points were detected in the a-chain A2 of glycinin as well as in the a'-chain of P-conglycinin. From the known three-dimensional structure of 7 s globulin and the hypothetical model of 7 s globulin-like 11s globulin structure, it was possible to draw the conclusion that two distinct types of susceptible sites for proteolytic cleavage are characteristic of the subunits of both globulins. The first includes the sequences linking N-and C-terminal domains of both globulins and the sequence of N-terminal extensions of 70-kDa subunits from the vicilinlike 7 s globulins. The second type includes the loop between P-strands E and F of the N-terminal domain of 11s globulins and of the C-terminal domain of 7 s globulins. A statistically significant similarity was found between the N-terminal extension of the a'-chain of P-conglycinin and the interdomain linker regions of soybean glycinin and pea legumin. It is proposed that the three sequence regions which form the first type of susceptible sites are of similar structural function and might have evolved from the Nterminal segment of a putative single-domain ancestor.Keywords: protein structure ; seed storage globulins ; gene evolution ; limited proteolysis ; Glycine rnax (L.) Merr.Glycinin and P-conglycinin from soybean seeds belong to the legumin-like 11s and vicilin-like 7s storage globulin families, respectively. Secondary structure predictions and multiple alignment of amino acid sequences [I] suggest that structural similarities should exist between 1 IS and 7s seed storage globulins. The trimer which is formed from 11s globulin subunit precursors before their cleavage into a-and /)-chains [2, 31 as well as the trimeric half-molecule from the mature hexameric 11s globulin holoprotein [4] appear to be structurally similar to the trimeric 7 s globulin molecule. X-ray-crystallographic analysis of two 7 s globulins, canavalin from jack bean [5] and phaseolin from garden bean [6, 71, revealed that their subunits are composed of two similar domains. Each domain is composed of a /]-barrel followed by a region of a-helices (Fig. 1, A1 and BI).A canonical model for the domain structure of 7 s globulins, including both 50-kDa and 70-kDa subunits, was postulated 171. However, the structural role of the extended N-terminal sequence upstream from the N-terminal domain of the 70-kDa subunits remains unclear. Different alignment methods that have been employed to compare the domains of the 7 s globulin subunits with corresponding regions from the 11s globulin subunits suggest that similar N-and C-terminal domains should exist in the legumin-like storage globulins [7, 81 (Fig. 1, A2 has been predicted that all four stru...

11S protein of the sunflower seed is precipitated by phytate at pH 2.0, a protein‐phytate complex being formed thereby. The number of the phosphate groups bound by the time the precipitation is completed is less than one half of that of the basic groups of the 11S protein. The insolubility of the complex formed interferes with the acid extraction of protein from the sunflower meal and solvent cake. The protein extractability increases sharply after the removal of the phytate.

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The modification of slightly soluble sunflower protein isolates by superlimited proteolysis (-0.1 % splitting of the peptide bonds) raises 1 S-2-fold their solubility in neutral medium. The modified preparations may be isolated by isoelectric precipitation with a yield of 95-98 % and became capable to form thermotropic gels.The yields of the isolates obtained from industrial solvent cake are lower (80-82%). The expenditure of proteinase is one order lower than in the usually employed methods of limited proteolysis and the duration of the process is several times lower.