No description available.

The sweet potato has become a major international crop and it is also the main staple food for many people in the developing world. This crop is desirable as it is high yielding, easy to grow and has a low cost of production. However, the tubers have a low protein content and a low concentration of amino acids, particularly the aspartate amino acid. This has contributed to malnutrition in some areas. To help overcome this problem this study had the aim of producing lines of sweet potato with increased nutritional values. Two varieties, Beauregard and LO322, were selected for study as they have a good flavour and a high beta-carotene content. The conditions for the tissue culture of these varieties were determined by altering the mineral and hormonal composition of the culture medium. Increases in nutritional composition were induced by treating calli with mutagenic agents which included : colchicine, ethylmethanesulphonate, UV radiation and two levels of gamma radiation. Putative mutants with reduced feedback inhibition in the pathways which lead to the synthesis of the aspartate amino acids were selected by placing calli on media containing increasing concentrations of lysine and threonine. During the final stage of the selection process, calli were placed on a medium without the addition of selection agents. The results from the tissue culture study suggest that media, 2, 4-D and explant size affect callus growth. MSMA medium (a modified Murashige and Skoog medium) was the most suitable for growing the callus of Beauregard whilst modified White's medium (MW) was better for the growth of LO322 calli. The most prolific callus growth was exhibited by explants of the cultivar Beauregard when placed on MSMA medium. This combination was used to determine the potential of mutagenic treatments to improve the nutritional qualities of the sweet potato. Results from treatments with mutagenic agents showed that all mutagens used had the capability of increasing the soluble protein content of callus. These treatments also had the capacity to increase the concentration of aspartate and other amino acids. Of the mutagens trialed, a treatment with 500 rad gamma radiation appears to be the most suitable for increasing protein and amino acid concentrations. Therefore, once the conditions for regeneration of shoots from calli have been determined this study suggests that it should be possible to produce lines of sweet potato with increased nutritional values using this agent / Master of Science (Hons)

The aim with this project was to evaluate Waters AccQTag method which was ananalytical method that Waters Corporation provides for determination of aminoacids. The amino acid analysis was carried out by reversed-phase AQUITY UPLCH-Class, using a BEH C18-column and a PDA detector.Both primary and secondary amino acids were analyzed after precolumnderivatization with the AccQTag reagent kit by a manual procedure and, detected at260 nm. Fresenius Kabis existing products, Aminoven 10 % and Vamin 18EF wereused as samples. The evaluation was based on external calibration curves withprepared standard solutions from Fresenius Kabi, with the addition of the internalstandard L-Norvaline. Waters amino acid standard was used for the system suitabilitytest. A validation according to the ICH guidelines were performed with the followingparameters: specificity, linearity, precision, LOQ, LOD and robustness.Complementary parameters for system suitability test (SST) and stability of standardand reagent were also evaluated. The validation showed that the % RSD values forspecificity, system suitability test and robustness were within the acceptance criteriaof equal or less than 3 % for amino acids. Although the precision were between1.3-7.5 % which was higher than the acceptance criteria of equal or less than 3 %, thiswas likely due to sensitive sample preparation. The linearity was bad which made itimpossible to quantify the method since the calibration curves were below 0.999. Itwas concluded that the system was robust and can be used to analyze amino acids inAminoven 10 % and Vamin 18EF but the preparation step should if possible beautomatized to achieve better precision in the analytical work. Two amino acids,cysteine and histidine, needs to be studied further; cysteine gave three peaks insteadof one and histidine gave a peak split at higher injection volume than 0.5 uL.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 1986.

A series of conformationally constrained and flexible pseudopeptides were prepared and their thermodynamic parameters on binding to the Grb2 SH2 domain were determined by isothermal titration calorimetry (ITC). Cyclopropane constrained analogs having hydrophobic amino acid residues at the pTyr+1 position exhibited, on average, a 2-5 fold improvement in binding affinities with the enhancement in affinities due to a more favorable enthalpy, not entropy, of binding. This serves as the first set of examples which demonstrate that favorable entropies of binding are not an inherent characteristic of ligand preorganization. Incorporation of polar amino acid residues at the pTyr+1 position eventuated in a slightly different thermodynamic effect than what was observed with the hydrophobic analogs. The constrained molecules exhibited greater binding affinities for the Grb2 SH2 domain and that increase in affinity was a consequence of a more favorable enthalpy, not entropy, of binding. However, the binding entropies for the polar set of constrained and flexible molecules were all negative. Structural information obtained from the co-crystallization of selected constrained and flexible ligand pairs with the Grb2 SH2 domain revealed an increase in conformational mobility of the BC loop in the complexes of the constrained derivatives and the presence of a greater number of direct polar contacts, but fewer water-mediated interactions between the phosphate group of the constrained molecules and the pTyr binding pocket of the domain. The construction of the cis-hydrindanone ring system in sieboldine A was accomplished utilizing either a Lewis acid-mediated silyl-directed Nazarov cyclization of a functionalized divinyl ketone or a sequential Ni(0)-catalyzed 1,4-addition/5-endo-dig cyclization. Propargylzinc bromide was shown to undergo conjugate addition to the [alpha]-aminopropyl substituted enone using Ni(acac)₂, thus providing a new, mild protocol for the conjugate propargylation reaction. Further efforts toward the formation of the α-epoxy ketone are described. / text

Not available / text

published_or_final_version / Biochemistry / Master / Master of Philosophy

published_or_final_version / Zoology / Master / Master of Philosophy

No description available.