published_or_final_version / abstract / toc / Paediatrics and Adolescent Medicine / Master / Master of Philosophy

No description available.

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

Genetic variants of milk proteins are the result of mutation causing substitutions or deletions of amino acids in the peptides. Certain variants are closely associated with milk production, milk composition and milk qualities such as heat stability and cheesemaking properties. All of the milk protein variants known so far, have been detected by electrophoresis because mutations which have occurred gave rise to changes in net charges. "Silent" variants involve amino acid substitutions which are not accompanied by charge differences and hence would not be identified by electrophoresis. The aim of this project was to search for silent variants of $ alpha sb{ rm s1}$-casein, $ beta$-casein and $ kappa$-casein by application of reversed-phase HPLC for the identification of mutants causing changes in hydrophobicities of peptides. / Whole casein from 281 Holstein and Ayrshire milk samples were fractionated by DEAE-cellulose ion-exchange chromatography, using an FPLC system. The pure forms of major caseins ($ alpha sb{ rm s1}$-casein, $ beta$-casein and $ kappa$-casein) were hydrolysed by trypsin and the digests obtained therefrom were resolved by reversed-phase HPLC. Comparison of peptide profiles within the same electrophoretic variant of homozygous caseins indicated that 24 out of 264 $ alpha sb{ rm s1}$-casein BB, 9 out of 57 $ beta$-casein A$ sp1$A$ sp1$, 5 out of 55 $ beta$-casein A$ sp2$A$ sp2$ and 8 out of 188 $ kappa$-casein AA could be classified as potential silent variants.

No description available.

Amendements: leaves 252-254. / Copies of author's previously published articles inserted. / Bibliography: leaves 226-251. / vi, 254 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The CYP2C19 and CYP2D6 genetic polymorphisms control the oxidative metabolism of many different drug classes. Populations are separated into groups of extensive metabolisers (EM), poor metabolisers (PM), and in the case of CYP2D6, ultra-rapid metabolisers (UM). In vitro studies using human liver microsomes were conducted to examine the kinetics of the oxidative metabolism of flunitrazepam, and which CYP450 enzymes mediate the oxidative metabolism of flunitrazepam, (S)-mephenytoin and proguanil. / Thesis (Ph.D.)--University of Adelaide, Dept. of Clinical and Experimental Pharmacology, 2000

Thesis (M. Res. (Med.))--University of Hong Kong, 2007.

Thesis (M.S. in Interdisciplinary Studies: Neurogenetics)--Vanderbilt University, Dec. 2007. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D. in Psychology)--Vanderbilt University, Dec. 2007. / Title from title screen. Includes bibliographical references.

Thesis (MSc)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.