Role of Disulfide Bonds upon the Structural Stability of an Amaranth Globulin

• Published in: Journal of agricultural and food chemistry Vol. 47; no. 8; pp. 3001 - 3008
• Main Authors: Castellani, Oscar F, Martínez, E. Nora, Añón, M. Cristina
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.08.1999
• Subjects: Animal, plant, fungal and microbial proteins, edible seaweeds and food yeasts; Biological and medical sciences; Calorimetry; Disulfides - chemistry; Drug Stability; Flour - analysis; Food industries; Fundamental and applied biological sciences. Psychology; Globulins - chemistry; Globulins - isolation & purification; Plants, Edible - chemistry; Research and development. New food products, dietetic foods and beverages; Seeds - chemistry; Differential scanning calorimetry; Structure stability; Molecular structure; Thiohydroxyl group; Experimental study; Protein; Globulin; Intermolecular interaction; Chemical reduction; Mercaptoalcohol; Amaranth; Disulfide bond; Plant protein; Intramolecular interaction
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf981252a

Analysis of globulin-P, the polymerized amaranth globulin, gave a low amount of free sulfhydryls (10.2 ± 0.5 μmol/g) from which 7 ± 1 μmol/g was buried inside the molecule. In addition, its disulfide content was high (51 ± 1 μmol/g) and similar to soybean 11S globulin content. The more exposed disulfide bridges were found to be stabilizing polymers, whereas the less reactive bridges were either linking P20 and P30 polypeptides or forming intrachain linkages. It was found that the buried bonds participate in the stabilization of folded polypeptides and the quaternary structure of the globulin. In turn, the dissociation of polymers and disruption of the quaternary structure by the action of 2-mercaptoethanol reverted upon removal of the reducing agent. This demonstrates that the polymerized state and the quaternary structure of the molecules are most favorable from the thermodynamic point of view. The similar content of SH and SS in globulin-P and globulin-S found in this laboratory suggests that the differences between these proteins may be ascribed to other compositional differences. Keywords: Amaranth globulins; sulfhydryl and disulfide groups; protein structure; calorimetry