Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 148-173). Available also in a digital version from Dissertation Abstracts.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb. 12, 2010 ). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dr. Robert L. Kallenbach, Thesis Supervisor. Includes bibliographical references.

Background Many studies in western countries have suggested a positive association between intake of trans fatty acid (TFA) and risk of cardiovascular diseases (CVDs). In Asia, although intake of TFA was relatively low, it evidenced an increasing trend which was accompanied with an increasing prevalence of CVDs among the population. There was currently no systematic review on the relationship between intake of TFA and CVDs in Asian population. This systematic review was aimed to synthesize the association between intake of TFA and the risk of CVDs in Asian population from published literature. Methods Both English and Chinese literature published before 1st January 2014were retrieved from PubMed, Medline, Google scholaand CNKI with a combination of keywords. Studies that reported the associations between intake of TFA and CVD-related risks and those conducted among Asian population were included. The quality of eligible literature included in the review was assessed based on STROBE. Findings regarding the associations between intake of TFA and risk of CVDs were extracted and synthesized through comparing and evaluating the quality of findings across the included studies. Results Of the 378 articles retrieved from the datasets, nine studies were eligible to be included in this systematic review. The nine studies covered six Asian countries including Iran, China, Korea, Japan, Israel and India. Seven of nine studies indicated a positive association between intake of TFA and risk of CVDs while the other two reported no significant association. However, none of the included studies were interventional studies and only one was prospective cohort study. Conclusion The findings that more intake of TFA was associated with increased risk of CVDs in Asian population were consistent with that in the western population. Specific regulations to restrict the use of TFA and interventions to promote public awareness of the health effects of TFA are recommended in Asian countries. Due to limited eligible studies that covered only six Asian countries, there remains cautious to generalize the findings to other Asian countries. / published_or_final_version / Public Health / Master / Master of Public Health

Flax (Linum usitatissimum L.) is one of the richest plant sources of omega-3 fatty acids praised for their health benefits. In this study, the extent of the genetic variability for genes encoding stearoyl-ACP desaturase (SAD), fatty acid desaturase 2 (FAD2) and 3 (FAD3) was determined by sequencing the six paralogous genes from 120 flax accessions representing a broad range of germplasm including some EMS mutant lines. A total of 6 alleles for sad1 and sad2, 21 for fad2a, 5 for fad2b, 15 for fad3a and 18 for fad3b were identified. Deduced amino acid sequences of the alleles predicted 4, 2, 3, 4, 6, and 7 isoforms, respectively. Allele frequencies varied greatly across genes. Fad3a, with 110 SNPs and 19 indels, and fad3b, with 50 SNPs and 5 indels, showed the highest levels of genetic variation. While most of the SNPs and all the indels were silent mutations, both genes carried non-sense SNP mutations resulting in premature stop codons, a feature not observed in sad and fad2 genes. Some alleles and isoforms discovered in induced mutant lines were absent in the natural germplasm. Correlation of these genotypic data with fatty acid composition data of 120 flax accessions phenotyped in six field experiments revealed statistically significant correlations of some of the SAD and FAD isoforms on fatty acid composition, oil content and iodine value. The novel allelic variants and isoforms identified for the six desaturases will be a resource for the development of oilseed flax with unique and useful fatty acid profiles. / October 2015

published_or_final_version / Chemistry / Master / Master of Philosophy

Oat is known to synthesize several epoxy fatty acids in seeds using peroxygenase (PXG), a type of hydroperoxide-dependent epoxygenase. This thesis aims to molecularly clone and functionally characterize the PXG genes from oat developing seeds. The research started with identifying additional PXG genes from oat expressed sequence tag (EST) databases using a previously identified oat peroxygenase AsPXG1 as a query sequence. This resulted in the identification of six homologous contig sequences from the EST data bases. Of them, two contigs with high sequence similarity and alignment with plant PXG/caleosin proteins were selected for cloning and functional analysis. Rapid amplification of cDNA ends (RACE) and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to retrieve the full length cDNAs of the contigs, which resulted in identification of three putative PXG genes, AsPXG2, AsPXG3 and AsPXG4. Open reading frame (ORF) of AsPXG2 is 702 bp long encoding a polypeptide of 233 amino acids, while ORFs of both AsPXG3 and AsPXG4 are 627 bp in length coding for 208 amino acids. All these putative peroxygenases comprise a single transmembrane domain, presumably for lipid droplet anchoring, conserved hisditine residues for heme-binding and a conserved EF-hand motif for calcium-binding. To functionally characterize the three genes, their ORFs were individually expressed in Escherichia coli/Pichia pastoris. The enzymatic assays showed that all transformants produced 9,10-epoxystearic acid methyl ester in the presence of oleic acid methyl ester and cumene hydroperoxide, indicating all three genes encode functional peroxygenase. AsPXG3 has the highest specific activity at 42 mol/mg/min with about 25% substrate conversion efficiency. Substrate specificity assays on free fatty acids showed that AsPXG3 could epoxidize all mono- and poly-unsaturated fatty acids tested, with linolenic acid (C18:3-9c,12c,15c) being the most preferred substrate. Site-directed mutagenesis of three conserved histidines and nine conserved residues surrounding the histidines in AsPXG3 showed that substitution of the first conserved histidine at position 32 (H1) and the third conserved histidine at position 102 (H3) with alanine respectively resulted in complete loss of the enzymatic activity, while substitution of the second conserved histidine at position 98 (H2) resulted in only slight reduction of the activity, indicating that only H1 and H3 are absolutely essential and probably involved in heme-binding for the peroxygenase. Substitution of leucine at position 29 (M1), isoleucine at position 97 (M5), and lysine at position 101 (M8) with alanine reduced the enzymatic activity on oleic acid methyl ester by more than 80% relative to the wild type enzyme, indicating these three residues are also very important for catalytic activity. The activity of M1, M5 and M8 mutants was also drastically reduced on all other free mono-unsaturated fatty acids tested (>60%). However, to linolenic acid, M5 showed only slight reduction of the activity (~15%) and M8 even increased the activity by 12% relative to the wild type enzyme. These results suggest that these conserved residues might play roles in defining the shape and size of the catalytic site for interaction of the heme with fatty acid substrates.

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