Thesis (Ph. D.)--University of Wisconsin--Madison, 1952. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Bibliographies: leaves 8-9, [103]-109.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1950. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 100-109).

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 82-89).

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

The control of milk protein production was investigated utilising two different approaches. The first model is one of intravenous infusion of atropine. Atropine, which decreases milk protein yield, has been theorised to act either by decreasing blood somatotropin (ST) concentration or by decreasing blood amino acid (AA) concentration. Thus, the first experiment was designed to test which mechanism, or both, is responsible for the effects on milk protein yield. Five lactating dairy cows were assigned to the following treatments which were administered intravenously: Saline (CONT), atropine (ATR), ATR + ST, ATR + AAs, and ATR + ST + AAs. Atropine treatment failed to decrease plasma ST concentration but did decrease plasma alpha-amino nitrogen concentration. Atropine treatment decreased milk protein yield but neither ST, AAs, nor ST + AAs were able to maintain milk protein yield at the CONT level when infused with ATR. It is clear that the treatments tested are not directly responsible for the decrease in milk protein yield due to ATR. Therefore, neither ST, AAs, nor ST + AAs appear to have direct control of milk protein production. Plasma insulin (INS) concentration was decreased and plasma IGF-I concentration was not decreased by ATR treatment. Insulin, therefore, presents itself as a candidate for direct control over milk protein synthesis. The second model is one of monitoring endocrine response to abomasal infusion of AAs mimicking the profile of milk protein with selective deletion of certain AAs. Six lactating dairy cows were subjected to the following treatments: Saline (negative control, NC), AAs (positive control, PC), PC minus methionine (PC-Met), PC minus lysine (PC-Lys), PC minus histidine (PC-His), and PC minus the branched-chain AAs (PC-BCAAs). All endocrine factors studied (ST, INS, glucagon & IGF-I) were affected by treatment. Plasma IGF-I concentration responded similarly, except for the PC-Met treatment, to milk protein yield (Weekes and Cant, 200

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.

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