PubMed Health⌕ Search

Biomedical subjects

David A Mitchell

Publications and source records attributed to David A Mitchell.

18 recordsLinked to original sources
PubMed2026

The role of psychological resilience in the relationship between complex post-traumatic stress disorder symptom severity and functioning impairment in mental health support-seeking Australian defence force veterans: A cross-sectional study.

OBJECTIVE: Military veterans have high rates of mental health conditions; complex post-traumatic stress disorder may be the most functionally impaired trauma diagnosis in this patient group. Psychological resilience acts as a protective factor for mental health. Still, it is unclear how this may influence relationships between the two main symptom clusters of complex post-traumatic stress disorder and functioning impairment in veterans. Therefore, we investigated the relationships between psychological resilience, trauma symptom severity, trauma exposure and work/social functional impairment among Australian Defence Force veterans. METHODS: Cross-sectional survey including 148 mental health support-seeking former-serving Australian Defence Force veterans in primary care. Relationships between variables were explored using correlations, mean difference tests and mediation analysis to examine the role of resilience in the relationship between complex post-traumatic stress disorder symptoms and functional impairment. RESULTS: Resilience showed significant negative correlations with functioning impairment. The number of traumas showed weak positive correlations with disturbances in self-organisation symptoms, post-traumatic stress disorder symptoms and functional impairment. The complex post-traumatic stress disorder group had significantly lower resilience and functioning than those with no diagnosis. After controlling for the number of trauma exposures, resilience partially mediated the association between post-traumatic stress disorder symptoms and functioning (indirect effect&#x2009;=&#x2009;0.141, p&#x2009;<&#x2009;0.05), and partially mediated the association between disturbances in self-organisation symptoms and functioning (indirect effect&#x2009;=&#x2009;0.157, p&#x2009;<&#x2009;0.05). CONCLUSIONS: Psychological resilience was associated with better functioning in veterans regardless of trauma diagnosis. Resilience also partially mediates the relationship between disturbances in self-organisation/post-traumatic stress disorder symptoms and functioning in those with International Classification of Diseases, 11th Revision, complex post-traumatic stress disorder, indicating it is an important intervention target in Australian Defence Force veterans with polytrauma.

Humans↗
PubMed2006

Protein palmitoylation by a family of DHHC protein S-acyltransferases.

Protein palmitoylation refers to the posttranslational addition of a 16 carbon fatty acid to the side chain of cysteine, forming a thioester linkage. This acyl modification is readily reversible, providing a potential regulatory mechanism to mediate protein-membrane interactions and subcellular trafficking of proteins. The mechanism that underlies the transfer of palmitate or other long-chain fatty acids to protein was uncovered through genetic screens in yeast. Two related S-palmitoyltransferases were discovered. Erf2 palmitoylates yeast Ras proteins, whereas Akr1 modifies the yeast casein kinase, Yck2. Erf2 and Akr1 share a common sequence referred to as a DHHC (aspartate-histidine-histidine-cysteine) domain. Numerous genes encoding DHHC domain proteins are found in all eukaryotic genome databases. Mounting evidence is consistent with this signature motif playing a direct role in protein acyltransferase (PAT) reactions, although many questions remain. This review presents the genetic and biochemical evidence for the PAT activity of DHHC proteins and discusses the mechanism of protein-mediated palmitoylation.

Acetyltransferases↗
PubMed2006

Cytochrome b(5) is a major reductant in vivo of human indoleamine 2,3-dioxygenase expressed in yeast.

The evolutionary relationship of indoleamine 2,3-dioxygenase (IDO) to some gastropod myoglobins suggests that IDO may undergo autoxidation in vivo such that one or more currently unidentified electron donors are required to maintain IDO heme iron in the active, ferrous state. To evaluate this hypothesis we have used yeast knockout mutants in combination with a recently developed yeast growth assay for IDO activity in vivo to demonstrate a role for cytochrome b(5) and cytochrome b(5) reductase in maintaining IDO activity in vivo.

Cytochrome-B(5) Reductase↗
PubMed2005

TFII-I and USF (RBF-2) regulate Ras/MAPK-responsive HIV-1 transcription in T cells.

The HIV-1 long terminal repeat (LTR) is stringently controlled by T cell activation signals, and binds a variety of transcription factors whose activities are regulated downstream of the T cell receptor. One of the most highly conserved cis-elements on the LTR, designated RBEIII, binds the factor RBF-2 which is comprised of a USF-1/USF-2 heterodimer and a co-factor TFII-I. RBF-2 is necessary for transcription from the LTR in response to RAS-MAPK activation through T cell receptor engagement, but is also required for repression of viral expression in unstimulated cells. Considering the defined activities of USF and TFII-I, RBF-2 may be responsible for regulating promoter context by controlling chromatin organisation, thereby coordinating opportunity for transcriptional activation by additional factors bound to the enhancer region.

Cell Communication↗
PubMed2005

Thromboelastographic study of the effect of manipulation of central veins on coagulability of venous blood.

AIM: To measure whole blood coagulability in vitro using thromboelastography before and after direct and indirect manipulation of the internal jugular and subclavian veins. METHODS: We studied 10 patients (American Society of Anaesthesiologists (ASA) grades I or II) with malignant disease of the head and neck who were having selective neck dissections. We excluded patients with diabetes, those who were being given any anticoagulant, those who were actively infected, and those with known coagulopathy. We took 3 ml samples of venous blood during insertion of a peripheral cannula, after insertion of a central venous cannula, and after dissection of the internal jugular vein. Thromboelastography was done on recalcified citrated samples within 1h of sampling. The variables r, k, alpha angle, and maximum amplitude were recorded at each point and the values before and after manipulation were compared using t-tests. RESULTS: The only change was seen in the variable r, which showed an insignificant increase in coagulability.

Blood Coagulation↗
PubMed2004

Thermal denaturation: is solid-state fermentation really a good technology for the production of enzymes?

The potential for thermal denaturation to cause enzyme losses during solid-state fermentation processes for the production of enzymes was examined, using the protease of Penicillium fellutanum as a model system. The frequency factor and activation energies for the first-order denaturation of this enzyme were determined as 3.447 x 10(59) h(-1) and 364,070 Jmol(-1), respectively. These values were incorporated into a mathematical model of enzyme deactivation, which was used to investigate the consequences of subjecting this protease to temporal temperature profiles reported in the literature for mid-height in a 34 cm high packed-bed bioreactor of 150 mm diameter. In this literature source, temperature profiles were measured for 5, 15 and 25 liters per minute of air and enzyme activities were measured as a function of time. The enzyme activity profiles predicted by the model were distributed similarly, one relative to the other, as had been found in the experimental study, with substantial amounts of denaturation being predicted when the substrate temperature exceeded 40 degrees C, which occurred at the lower two airflow rates. A mathematical model of a well-mixed bioreactor was used to explore the difficulties that would be faced at large scale. It suggests that even with airflows as high as one volume per volume per minute, up to 85% of the enzyme produced by the microorganism can be denatured by the end of the fermentation. This work highlights the extra care that must be taken in scaling up solid-state fermentation processes for the production of thermolabile products.

Bioreactors↗
PubMed2004

Mucinous intestinal type adenocarcinoma of the sinonasal tract secondary to passive wood dust inhalation: case report.

A 76-year-old female patient with a mucinous intestinal type adenocarcinoma of the sinonasal tract is described. The probable aetiology of passive hard wood dust inhalation, investigations carried out and subsequent surgical treatment using a transfacial access approach and a temporoparietal fascial composite free flap in conjunction with free auricular cartilage are described.

Adenocarcinoma, Mucinous↗
PubMed2003

Use of confocal scanning laser microscopy to measure the concentrations of aerial and penetrative hyphae during growth of Rhizopus oligosporus on a solid surface.

In order to develop a method for use in investigations of spatial biomass distribution in solid-state fermentation systems, confocal scanning laser microscopy was used to determine the concentrations of aerial and penetrative biomass against height and depth above and below the substrate surface, during growth of Rhizopus oligosporus on potato dextrose agar. Penetrative hyphae had penetrated to a depth of 0.445 cm by 64 h and showed rhizoid morphology, in which the maximum biomass concentration, of 4.45 mg dry wt cm(-3), occurred at a depth of 0.075 cm. For aerial biomass the maximum density of 39.54 mg dry wt (-3) occurred at the substrate surface. For both aerial and penetrative biomass, there were two distinct regions in which the biomass concentration decayed exponentially with distance from the surface. For aerial biomass, the first exponential decay region was up to 0.1 cm height. The second region above the height of 0.1 cm corresponded to that in which sporangiophores dominated. This work lays the foundation for deeper studies into what controls the growth of fungal hyphae above and below the surfaces of solid substrates.

Biomass↗
PubMed2003

Use of confocal microscopy to follow the development of penetrative hyphae during growth of Rhizopus oligosporus in an artificial solid-state fermentation system.

Two methods were compared for determining the concentration of penetrative biomass during growth of Rhizopus oligosporus on an artificial solid substrate consisting of an inert gel and starch as the sole source of carbon and energy. The first method was based on the use of a hand microtome to make sections of approximately 0.2- to 0.4-mm thickness parallel to the substrate surface and the determination of the glucosamine content in each slice. Use of glucosamine measurements to estimate biomass concentrations was shown to be problematic due to the large variations in glucosamine content with mycelial age. The second method was a novel method based on the use of confocal scanning laser microscopy to estimate the fractional volume occupied by the biomass. Although it is not simple to translate fractional volumes into dry weights of hyphae due to the lack of experimentally determined conversion factors, measurement of the fractional volumes in themselves is useful for characterizing fungal penetration into the substrate. Growth of penetrative biomass in the artificial model substrate showed two forms of growth with an indistinct mass in the region close to the substrate surface and a few hyphae penetrating perpendicularly to the surface in regions further away from the substrate surface. The biomass profiles against depth obtained from the confocal microscopy showed two linear regions on log-linear plots, which are possibly related to different oxygen availability at different depths within the substrate. Confocal microscopy has the potential to be a powerful tool in the investigation of fungal growth mechanisms in solid-state fermentation.

Biofilms↗
PubMed2003

Synthetic lethal analysis implicates Ste20p, a p21-activated potein kinase, in polarisome activation.

The p21-activated kinases Ste20p and Cla4p carry out undefined functions that are essential for viability during budding in Saccharomyces cerevisiae. To gain insight into the roles of Ste20p, we have used a synthetic lethal mutant screen to identify additional genes that are required in the absence of Cla4p. Altogether, we identified 65 genes, including genes with roles in cell polarity, mitosis, and cell wall maintenance. Herein, we focus on a set that defines a function carried out by Bni1p and several of its interacting proteins. We found that Bni1p and a group of proteins that complex with Bni1p (Bud6p, Spa2p, and Pea2p) are essential in a cla4delta mutant background. Bni1p, Bud6p, Spa2, and Pea2p are members of a group of polarity determining proteins referred to as the polarisome. Loss of polarisome proteins from a cla4delta strain causes cells to form elongated buds that have mislocalized septin rings. In contrast, other proteins that interact with or functionally associate with Bni1p and have roles in nuclear migration and cytokinesis, including Num1p and Hof1p, are not essential in the absence of Cla4p. Finally, we have found that Bni1p is phosphorylated in vivo, and a substantial portion of this phosphorylation is dependent on STE20. Together, these results suggest that one function of Ste20p may be to activate the polarisome complex by phosphorylation of Bni1p.

Base Sequence↗
PubMed2003

Palmitoylation and plasma membrane localization of Ras2p by a nonclassical trafficking pathway in Saccharomyces cerevisiae.

Subcellular localization of Ras proteins to the plasma membrane is accomplished in part by covalent attachment of a farnesyl moiety to the conserved CaaX box cysteine. Farnesylation targets Ras to the endoplasmic reticulum (ER), where additional processing steps occur, resulting in translocation of Ras to the plasma membrane. The mechanism(s) by which this occurs is not well understood. In this report, we show that plasma membrane localization of Ras2p in Saccharomyces cerevisiae does not require the classical secretory pathway or a functional Golgi apparatus. However, when the classical secretory pathway is disrupted, plasma membrane localization requires Erf2p, a protein that resides in the ER membrane and is required for efficient palmitoylation of Ras2p. Deletion of ERF2 results in a Ras2p steady-state localization defect that is more severe when combined with sec-ts mutants or brefeldin A treatment. The Erf2p-dependent localization of Ras2p correlates with the palmitoylation of Cys-318. An Erf2p-Erf4p complex has recently been shown to be an ER-associated palmitoyltransferase that can palmitoylate Cys-318 of Ras2p (S. Lobo, W. K. Greentree, M. E. Linder, and R. J. Deschenes, J. Biol. Chem. 277:41268-41273, 2002). Erf2-dependent palmitoylation as well as localization of Ras2p requires a region of the hypervariable domain adjacent to the CaaX box. These results provide evidence for the existence of a palmitoylation-dependent, nonclassical endomembrane trafficking system for the plasma membrane localization of Ras proteins.

Acyltransferases↗
PubMed2002

The potential for establishment of axial temperature profiles during solid-state fermentation in rotating drum bioreactors.

The mixing and heat transfer phenomena within rotating drum bioreactors (RDBs) used for solid-state fermentation processes are poorly studied. The potential for the establishment of axial temperature gradients within the substrate bed was explored using a heat transfer model. For growth of Aspergillus oryzae on wheat bran within a 24 L RDB with air at a superficial velocity of 0.0023 m s(-1) and 15% relative humidity, the model predicts an axial gradient between the air inlet and outlet of 2 degrees C during rapid growth, compared to experimental axial temperature gradients of between 1 and 4 degrees C. Undesirably high temperatures occur throughout the bed under these operating conditions, but the model predicts that good temperature control can be achieved using humid air (90% relative humidity) at superficial velocities of 1 m s(-1) for a 204 L RDB. For a 2200 L RDB, good temperature control is predicted with superficial velocities as low as 0.4 m s(-1) with the airflow being switched from 90% to 15% relative humidity whenever the temperature at the outlet end of the drum exceeds the optimal temperature for growth. This work suggests that significant axial temperature gradients can arise in those RDBs that lack provision for axial mixing. It is therefore advisable to use angled lifters within RDBs to promote axial mixing.

Air Movements↗
PubMed2002

A two-phase model for water and heat transfer within an intermittently-mixed solid-state fermentation bioreactor with forced aeration.

A two-phase dynamic model is developed that describes heat and mass transfer in intermittently-mixed solid-state fermentation bioreactors. The model predicts that in the regions of the bed near the air inlet there can be significant differences in the air and solid temperatures, while in the remainder of the bed the gas and solid phases are much closer to equilibrium, although there can be differences in water activity of around 0.05. The increase in the temperature of the gas as it flows through the bed means that it is impossible to prevent the bed from drying out, even if saturated air is used at the air inlet. The substrate can dry to water activities that severely limit growth, unless the bed is intermittently mixed, with the addition of water to bring the water activity back to the desired value. Under the conditions assumed for the simulation, which was designed to mimic the growth of Aspergillus niger on corn, two mixing events were necessary, one at 17.4 and the other at 27.9 h. Even though such a strategy can minimize the restriction of growth by water-limitation, temperature-limitation remains a problem due to the rapid heating dynamics. The model is obviously a useful tool that can be used to guide scale-up and to test control strategies. Such a model, describing the non-equilibrium situation between the gas and solid phases, has not previously been proposed for solid-state fermentation bioreactors. Models in the literature that assume gas-solid temperature and moisture equilibrium cannot describe the large temperature differences between the gas and solid phase which occur within the bed near the air inlet.

Air Movements↗
PubMed2002

Mass transfer correlations for rotating drum bioreactors.

Evaporative cooling is extremely important for large-scale operation of rotating drum bioreactors (RDBs). Outlet water vapour concentrations were measured for a RDB containing wet wheat bran with the aim of determining the mass transfer coefficient for evaporation from the bran bed to the headspace. Mass transfer was expressed as the mass transfer coefficient times the area for transfer per unit volume of void space in the drum. Values of ka' were determined under combinations of aeration superficial velocities ranging from 0.006 to 0.017 ms(-1) and rotation rates ranging from 0 to 9 rpm. Mass transfer coefficients were evaluated using a variety of residence time distributions (RTDs) for flow in the gas phase including plug flow and well-mixed and a Central Jet RTD based on RTD studies. If plug flow is assumed, the degree of holdup at low effective Peclet (Pe(eff)) numbers gives an apparent under-estimate of ka' compared with empirical correlations. Values of ka' calculated using the Central Jet RTD agree well with values of ka' from literature correlations. There was a linear relationship between ka' and effective Peclet number: ka' = 2.32 x 10(-3)Pe(eff).

Bioreactors↗
PubMed2002

"Superhumanized" antibodies: reduction of immunogenic potential by complementarity-determining region grafting with human germline sequences: application to an anti-CD28.

Humanized Abs are created by combining, at the genetic level, the complementarity-determining regions of a murine mAb with the framework sequences of a human Ab variable domain. This leads to a functional Ab with reduced immunogenic side effects in human therapy. In this study, we report a new approach to humanizing murine mAbs that may reduce immunogenicity even further. This method is applied to humanize the murine anti-human CD28 Ab, 9.3. The canonical structures of the hypervariable loops of murine 9.3 were matched to human genomic V gene sequences whose hypervariable loops had identical or similar canonical structures. Framework sequences for those human V genes were then used, unmodified, with the 9.3 complementarity-determining regions to construct a humanized version of 9.3. The humanized 9.3 and a chimeric 9.3 control were expressed in Escherichia coli as Fab. The humanized Fab showed a moderate loss in avidity in a direct binding ELISA with immobilized CD28-Ig fusion protein (CD28-Ig). Humanized 9.3 blocked ligation of CD28-Ig to cells expressing the CD28 receptor CD80. Lastly, the humanized 9.3 showed biological activity as an immunosuppressant by inhibiting a MLR.

Amino Acid Sequence↗
PubMed2002

Overview of solid state bioprocessing.

Solid-state fermentation has centuries of history, but it is only in the last two decades that there has been a concerted effort to understand the bioprocessing issues involved and to apply them to a wide range of new products. This article provides an overview of the knowledge of solid-state bioprocessing that has been gained over this time. It shows that, although significant advances have been achieved in understanding of what controls process performance, much research is still required.

Bioreactors↗