Soy glycinin Influence of pH and ionic strength on solubility and molecular structure at ambient temperatures
article
This study describes the relationship between the solubility of glycinin, a major soy protein, and its structural properties at a quaternary, tertiary, and secondary folding level under conditions representative for food products. When the ionic strength is lowered from 0.5 to 0.2 or 0.03, the basic polypeptides shift more to the exterior of the glycinin complex, as determined at pH 7.6 by labeling solvent-exposed lysines, supported by the study of the proteolytic action of clostripain on glycinin. This structural reorganization caused the pH of minimal solubility to shift to higher values. Ultracentrifugational analysis shows that at pH 7.6 and an ionic strength of 0.5 glycinin forms hexameric complexes (11S), whereas at pH 3.8 and at anionic strength of 0.03 glycinin exists as trimers (7S). Intermediate situations are obtained by modulation of pH and ionic strength. The observed quaternary dissociation correlates with an increased amount of nonstructured protein at a secondary level and with changes in tertiary folding as determined using circular dichroism. Tryptophan fluorescence shows no significant structural changes for different ionic strengths but demonstrates a more tightly packed fluorophore environment when the pH is lowered from 7.6 to 3.8. Chemicals / CAS glycinin, 9007-93-6; soybean protein, 9010-10-0; Globulins; Plant Proteins; Soybean Proteins; glycinin, 9007-93-6.
Topics
GlycininIonic strengthPHSoysoybean proteinvegetable proteinchemistrycircular dichroismfood processingnonhumanosmolarityprotein denaturationprotein quaternary structurestructure analysisGlobulinsHydrogen-Ion ConcentrationOsmolar ConcentrationPlant ProteinsProtein FoldingProtein Structure, QuaternaryProtein Structure, SecondaryProtein Structure, TertiarySolubilitySoybean ProteinsSoybeansThermodynamics
TNO Identifier
953482
ISSN
00218561
Source
Journal of Agricultural and Food Chemistry, 48(6), pp. 1985-1990.
Pages
1985-1990
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