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Site Directed Mutagenesis of β-Ketoadipate Succinyl-Coenzyme A Transferase II from Acinetobacter Calcoaceticus (open access)

Site Directed Mutagenesis of β-Ketoadipate Succinyl-Coenzyme A Transferase II from Acinetobacter Calcoaceticus

The role of specific amino acid residues in β-ketoadipate succinyl-coenzyme A transferase II from Acinetobacter calcoaceticus was investigated. A 1412 base pair BamiHI-EcoRI fragment carrying the catIJ genes was amplified by polymerase chain reaction and inserted into pUCl9 to generate the plasmid pCATEl9. Escherichia coli DH5α (pCATEl9) carrying only the catlJ genes expressed 3-fold higher enzyme activity than the parent strain. Two mutants were constructed by site directed mutagenesis so that glutamate was replaced by a glutamine at positions Gln155 and Gln193 in the ß subunit of the primary amino acid sequence of the CoA transferase. Both mutants produced transferase that was catalytically active suggesting that Glu155 and Glu193 do not participate directly in catalysis.
Date: August 1993
Creator: Sheng, Mei
System: The UNT Digital Library
Nesting Ecology and Reproductive Correlates in the Desert-nesting Gray Gull Larus Modestus (open access)

Nesting Ecology and Reproductive Correlates in the Desert-nesting Gray Gull Larus Modestus

General objectives of my study were to describe the reproductive ecology of gray gulls in the large Lealtad colony, with emphasis on demographic parameters and physiological adaptations of eggs and chicks, which would complete some original objectives established in the early 1980's by Guerra and Fitzpatrick. Specifically, my study focused on describing, then comparing with other desert and non-desert nesting larids, interactive effects of ambient physical conditions and nest-site predation on eggs and chicks.
Date: May 1993
Creator: Aguilar Pulido, Roberto E. (Roberto Eric)
System: The UNT Digital Library
Temporal and Spatial Comparisons of Ambient Toxicity of the Trinity River in Relationship to an Effluent (open access)

Temporal and Spatial Comparisons of Ambient Toxicity of the Trinity River in Relationship to an Effluent

A toxicological study was initiated because of concerns about allegations that the Texas Water Commission that effluent from the Dallas Central Wastewater Treatment Plant, which discharges into the Trinity River, was affecting downstream water quality. Monthly, flow-weighted composite effluent samples were collected. Grab samples were also collected upstream and downstream from the effluent from April 1989 to August 1991. Toxicity tests were conducted on these samples using Ceriodaphnia dubia as the test organism. Samples were collected four times during this study in which rainfall occurred prior to sampling. In every instance, this "first flush" of the watershed during a rising hydrograph was toxic to C. dubia upstream. Analyzing toxicity by season resulted in a statistically significantly lower neonate production in the effluent than in the river samples during the months of June, July, and August. This impact on neonate production was suspected of being caused by organic pesticides which are used for insect control on lawns. The effluent was never acutely toxic to C. dubia. Primarily, toxic occurrences in either the effluent or the river samples were primarily of a chronic nature. Overall, survival of C. dubia was affected more frequently at the upstream site than in the effluent or …
Date: December 1993
Creator: Hall, David B., 1958-
System: The UNT Digital Library
Autonomic Reflexes of the Heart During Acute Myocardial Ischemia (open access)

Autonomic Reflexes of the Heart During Acute Myocardial Ischemia

This study investigated whether acute myocardial ischemia of the anterior left ventricular wall induced an increase in cardiac sympathetic efferent nerve activity and thereby affected regional myocardial blood flow and contractile function.
Date: May 1993
Creator: Meintjes, André F. (André Francois)
System: The UNT Digital Library
An Interpretation of Archaic Medical Treatises (open access)

An Interpretation of Archaic Medical Treatises

Ancient peoples did not distinguish between philosophy, religion, and science. Scientific truth did not exist apart from divine truth. Any new idea, finding, or theory was assimilated into a monolithic mythological structure. This is one of the causes of the underestimation of ancient science: it is always packaged in a myth - the method of preserving information in an oral culture. The mythological medium allowed the preservation and dissemination of hard-won, empirical, scientific knowledge through generations of preliterate peoples. The context for mythological memorization, or simply tradition, needed to be easily and naturally acquired. The ideal context was the anthropomorphic context, the ontogenic context. This is the Grand Allegory - the anthropomorphization of information. Biomyths are essentially biological texts allegorized in esoteric language.
Date: May 1993
Creator: Wagers, William D. (William Delbert)
System: The UNT Digital Library
Functional Properties and Organization of Primary Somatosensory Cortex (open access)

Functional Properties and Organization of Primary Somatosensory Cortex

The physiological characteristics and organization of cat primary somatosensory cortex (SI) were studied in electrophysiological and anatomical experiments. In single cell recording experiments, quantitatively controlled mechanical stimuli were used to examine the responses of SI cortical neurons to the velocity component of skin or hair displacement. The firing frequency of most rapidly adapting neurons increased as stimulus velocity was increased. Rapidly adapting neurons were classified based on their response patterns to constant-velocity ramp stimuli. Neurons in these classes differed significantly in sensitivity to stimulus velocity and amplitude, adaptation rate, and spontaneous firing rate. The results suggest that frequency coding of stimulus displacement velocity could be performed by individual SI rapidly adapting neurons, and that the classes of rapidly adapting neurons may play different roles in sensation of tactile stimuli. Tract-tracing experiments were used to investigate the ipsilateral corticocortical connections of areas 3b and 2 in SI. Different patterns of connections were found for these areas: area 2 projects to areas 3b, 1, 3a, 5a, 4 and second somatosensory cortex (SII), and area 3b projects to areas 2, 1, 3a and SII. To further compare the organization of these areas, the thalamic input to the forepaw representation within each area was …
Date: December 1993
Creator: Esteky, Hossein
System: The UNT Digital Library
Eutrophication Monitoring and Prediction (open access)

Eutrophication Monitoring and Prediction

Changes in trophic status are often related to increases or decreases in the allocthonous inputs of nutrients from changes in land use and management practices. Lake and reservoir managers are continually faced with the questions of what to monitor, how to monitor it, and how much change is necessary to be considered significant. This study is a compilation of four manuscripts, addressing one of these questions, using data from six reservoirs in Texas.
Date: December 1993
Creator: Cairns, Stefan H., 1949-
System: The UNT Digital Library
Prediction of Post Mortem Interval from Degradation of Endogenous Nucleotides in Human Subjects (open access)

Prediction of Post Mortem Interval from Degradation of Endogenous Nucleotides in Human Subjects

High Performance Liguid Chromatography was used to measure degradation of nucleotides in human cadavers for the purpose of prediction of post mortem interval. Endogenous nucleotides were extracted from integumentary tissue of six(6) human cadavers using six percent(6%) tricholoacetic acid. Linear regression statistical techniques were used to determine linearity of degradation of various nucleotide pools.
Date: April 1993
Creator: Williams, John Burgess
System: The UNT Digital Library
Isolation and Characterization of the Operon Containing Aspartate Transcarbamoylase and Dihydroorotase from Pseudomonas aeruginosa (open access)

Isolation and Characterization of the Operon Containing Aspartate Transcarbamoylase and Dihydroorotase from Pseudomonas aeruginosa

The Pseudomonas aeruginosa ATCase was cloned and sequenced to determine the correct size, subunit composition and architecture of this pivotal enzyme in pyrimidine biosynthesis. During the course of this work, it was determined that the ATCase of Pseudomonas was not 360,000 Da but rather present in a complex of 484,000 Da consisting of two different polypeptides (36,000 Da and 44,000 Da) with an architecture similar to that of E. coli ATCase, 2(C3):3(r2). However, there was no regulatory polypeptide found in the Pseudomonas ATCase.
Date: May 1993
Creator: Vickrey, John F. (John Fredrick), 1959-
System: The UNT Digital Library
Regulation, Evolution, and Properties of the ato Qperon and its Gene Products in Escherichia coli (open access)

Regulation, Evolution, and Properties of the ato Qperon and its Gene Products in Escherichia coli

The regulation of short chain fatty acid metabolism has been examined. Metabolism of acetoacetate, and short chain fatty acids such as butyrate and valerate, is predicated upon the expression of genes of the ato operon. Acetoacetate induces expression of a CoA transferase (encoded by the atoDA genes) and expression of a thiolase (encoded by the atoB gene). Metabolism of saturated short chain fatty acids requires the activities of the transferase and thiolase and enzymes of 6-oxidation as well. Spontaneous mutant strains were isolated that were either constitutive or that were inducible by valerate or butyrate instead of acetoacetate.
Date: August 1993
Creator: Chen, Chaw-Yuan
System: The UNT Digital Library
Chronic Ventricular Sympathectomy : Effects on Myocardial Metabolism (open access)

Chronic Ventricular Sympathectomy : Effects on Myocardial Metabolism

Chronic ventricular sympathectomy elicits changes in the coronary circulation, myocardial oxygen consumption and size of infarction resulting fromcoronary occlusion. These changes indicate a change occurring in the basic metabolism of the heart in response to the removal of its sympathetic nervous input. This hypothesis was tested using two groups of dogs, a shamoperated control and a ventricular sympathectomized group. The sympathectomy procedure was an intrapericardial surgical technique which selectively removes ventricular sympathetic input. Four weeks after surgery, left ventricular tissue samples were obtained and rapidly frozen to -80°C. Selected metabolic variables were then compared between the two groups.
Date: August 1993
Creator: Adix Longlet, Nancy J.
System: The UNT Digital Library
Interactions between Carotid and Cardiopulmonary Baroreceptor Populations during Dynamic Exercise in Man (open access)

Interactions between Carotid and Cardiopulmonary Baroreceptor Populations during Dynamic Exercise in Man

During dynamic exercise the arterial baroreflexes have been thought to reset to the prevailing level of systemic pressure in order to modulate transient changes in blood pressure with the same sensitivity (gain) as at rest. To test this hypothesis, cardiovascular responses to dynamic exercise and carotid baroreflex responses to graded neck suction and neck pressure (NS/NP) were examined in seven men of moderate fitness (V02 = 41.4±3.6 ml O2*kg^-1*min^-1) during two levels (20% and 40% of peak oxygen uptake) of steady-state exercise. In addition, deactivation of cardiopulmonary baroreceptors has been thought to increase carotid baroreflex responsiveness in the quiescent state in man.
Date: May 1993
Creator: Potts, Jeffrey Thomas
System: The UNT Digital Library
Nesting Ecology of the Dickcissel (Spiza americana) on a Tallgrass Prairie Relict in North Central Texas (open access)

Nesting Ecology of the Dickcissel (Spiza americana) on a Tallgrass Prairie Relict in North Central Texas

Eighty-three species of vascular plants were inventoried on the prairie relict during peak dickcissel nesting. Based on foliar cover and occurrence frequency, the five dominant plants were heath aster (Aster ericoides), eastern gammagrass (Tripsacum dactyloides), little bluestem (Schizachyrium scoparium), sensitive briar (Schrankia roemeriana) and meadow dropseed (Sporobolus asper). Sixty-one percent of dickcissel nests were constructed on or immediately next to three plant species: eastern gammagrass, sensitive briar and green milkweed.
Date: May 1993
Creator: Steigman, Kenneth Lee
System: The UNT Digital Library
Habitat Evaluation Procedures at Ray Roberts Lake: an Analysis of the Relationship with Ecological Indicators and a Study of Observer and Temporal Variability (open access)

Habitat Evaluation Procedures at Ray Roberts Lake: an Analysis of the Relationship with Ecological Indicators and a Study of Observer and Temporal Variability

Habitat Evaluation Procedure data gathered at Ray Roberts Lake in 1989 and 1990 were analysed for temporal variability, observer variability and relationships between Habitat Units (HUs) and species density/diversity. observer variability within a group was analysed by cluster analysis and bootstrapping. Five out of 36 sites showed significant differences in Habitat Suitability Index (HSI) values within the group. A nonparametric Mann-Whitney test was used to analyze temporal variability. One of 6 sites showed a significant difference in HSI values between years. Using Spearman's Rank Correlation Coefficient, a correlation was found between indicator species density and HUs. No significant correlation was indicated between species diversity and HUs.
Date: December 1993
Creator: Wattrus, Jane M. (Jane Marie)
System: The UNT Digital Library
Immunotoxicity of Chromium Contaminated Soil in the Earthworm, Lumbricus Terrestris (open access)

Immunotoxicity of Chromium Contaminated Soil in the Earthworm, Lumbricus Terrestris

Objective was to assess the toxicity of chromium (Cr) contaminated soil (CS) using the earthworm Lumbricus terrestris. Specific aims were to determine: (1) survival (LC50); .(2) immunotoxicity as indicated by lysozyme activity, coelomocyte counts, secretory (SR) and erythrocyte rosette (ER) formation, and phagocytosis; and (3) compare effects of CS exposure with those of Cr spiked artificial soil (AS) . CS Cr concentration was 8.78 mg/g with 98.2% being Cr^3+ and 1.8% being Cr^6+. Using 14 d AS protocol the LC50 was 6.49% CS: AS mixture. CS concentrations of 0.5, 1.0, 2.5 and 5.0% were sublethal, whereas 6.25, 12.5, 25, 50 and 100% CS were lethal. Sublethal exposure caused no immuno- modulation. Exposure to 50% CS: AS mixture for 5 d caused reduced SR and ER formation. Exposure to AS spiked with 0.27% Cr for 5 d resulted in immunomodulation equivalent to 50% CS: AS mixtures. Results indicated the CS to be acutely toxic.
Date: May 1993
Creator: Mohammadian, Gholamreza
System: The UNT Digital Library