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Title: Studies on proteins of Gramineae : some of their chemical and physical properties and their relationship to genetical characteristics
Author: Sim, Alexander Kennedy
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1963
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1. A method of starch gel electrophoresis has been developed for the fractionation of wheat and related protein systems which allowed the resolution of up to 32 wheat protein components. 2. By using this technique to separate wheat protein fractions obtained by column electrophoresis in a density gradient, and by examination of the effects of solvents of different dielectric constant, it has been possible to establish with some certainty the validity of the fractions as separate, but not necessarily unimolecular, species. The involvement of protein -protein complexing has been suggested from solubility data. 3. Membrane filters and gel molecular sieves (Sephadex) have been used to obtain estimates of the molecular size of these protein components. A very wide molecular weight range was indicated. 4. Examination of the solubility characteristics of wheat proteins has shown that a proper classification cannot readily be made on this basis. Protein solubility depended largely on the conditions of extraction and may possibly be influenced by the gluten complex formation. 5. Starch gel electrophoresis has been used to study the effects of physical, chemical and biochemical factors on the wheat protein system. The proteins have been shown to possess considerable stability, being unaffected by heating, certain denaturing agents, ultrasonic treatment and δ- irradiation (8 K rad). Higher levels of s- irradiation (35.6 x 106 rad), however, led to extensive protein alteration. The inclusion of oxidising and reducing agents in doughs following industrial improving procedures, had no detectable effect on the protein system, while more prolonged treatment led to an apparent reduced solubility on oxidation and marked protein alteration on reduction. Rheological changes in gluten, brought about by lipid removal or phospholipase treatment were not reflected in terms of protein alteration, indicating the probable redox participation of lipids in gluten. Wheat proteins were readily degraded by papain attack, but were less sensitive to tryptic and peptic action. This may be due to the presence of inhibitors in the system. 6. Examination of flours and glutens of different physical characteristics has shown distinct differences in protein composition, but these could not be correlated with rheological data. 7. Wedge and adhering proteins isolated from wheat endosperm have been shown to contain a very different complement of protein components, indicating, with solubility data, probable protein - starch interactions. Air -classified flours similarly examined showed no distinct differences in protein composition. 8. The changes in the wheat protein system during the life cycle of the plant have been followed using the starch gel electrophoresis technique. Fractions of low electrophoretic mobility were progressively degraded during germination and progressively synthesised towards the end of the ripening period, indicating their probable role as storage proteins of the endosperm. In contrast, fractions of higher mobility were less affected during germination and were utilised at a later stage. Similarly, these components were synthesised first during ripening and remained at a relatively constant level during the build -up of apparently high molecular weight material. On the information available it was not possible to determine whether the fast -moving fractions represented the enzymes of the system or were precursors of larger components. 9. The endosperm proteins of various Graminae have been examined. Pronounced differences in protein composition were shown, the general distribution giving some indication of the relationship of the genus to wheat. 10. A comparison of the endosperm proteins of different wheat species and closely related genera has shown that certain protein fractions probably reflect the genetical characteristics of the species. Certain similarities in protein composition have been correlated with available genetical history. 11. A study of the endosperm proteins of several varieties of T. vulgare has shown distinct differences in the composition of fractions of low electrophoretic mobility. Although certain of these components may be typical of the variety, others may be influenced to some extent by environmental factors.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available