Genetic variants of milk proteins result from amino acid substitutions or small fragment deletion in the polypeptide chain. It is well documented that certain variants are closely related to milk production, milk composition and physico-chemical properties of milk such as heat stability and coagulation properties during cheesemaking. So far, all the genetic variants have been characterized by various electrophoretic methods. Therefore, only variants involving differences in net charges could be identified. Silent variants are the results of amino acid substitutions or deletions which do not accompany charge differences and hence remain undetected by conventional electrophoretic methods. The objective of the present project is to develop proper methodology to identify and characterize silent variants of milk proteins based on hydrophobic properties of amino acids. Individual caseins were isolated from 635 milk samples by anion-exchange chromatography and their electrophoretic phenotype was determined by polyacrylamide gel electrophoresis under alkaline and acidic conditions. Trypsin hydrolysis of alphas1-casein, beta-casein and kappa-casein followed by reversed-phase HPLC was performed to identify possible mutations causing changes in hydrophobicities of amino acids. Among 627 alphas1-casein BB, 415 kappa-casein AA, 158 beta-casein A1A1 and 128 beta-casein A2A 2 according to electrophoresis, it was possible to find 25, 11, 16 and 7 samples respectively as potential silent variants. Further analysis of the aberrant peptides from alphas1-casein BB, kappa-casein AA and beta-casein A2A2 by mass spectrometry did not confirm the existence of silent variants; whereas analysis of aberrant peptide from beta-casein A1A1 revealed a mutation resulting in an increase of 16 Da. Analysis of amino acid composition of this aberrant beta-casein A1A1 peptide 114--169 showed a Leu replacing a Pro residue. Results from amino acid sequencing confirmed this mutation to be located at pos
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.34946 |
| Date | January 1998 |
| Creators | Dong, Chin. |
| Contributors | Ng-Kwai-Hang, K. F. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Animal Science.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001610085, proquestno: NQ44413, Theses scanned by UMI/ProQuest. |
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