pH dependence of redox potential in c-type cytochromes

The midpoint redox potential (Em) of mitochondrial cytochrome c is independent of pH below pH9 (Rodkey & Ball, 1950). For several bacterial homologues of cytochrome c, however, Em is markedly influenced by pH between pH5 and 9; in the case of Pseudomonas aeruginosa cytochrome ᶜ551 , the pH dependence has been interpreted as being due to the redox state dependent ionisation of a haem propionic acid substituent, which has a pK of 6.3 in the oxidised form of of the cytochrome and 7.2 in the reduced form (Moore et al., 1980). The redox state imposed separation of the propionic acid pK values was suggested to occur through the electrostatic influence of the haem, which carries a net charge of +1 in the ferricytochrome but 0 net charge in the ferrocytochrome.In an extension of the studies initiated with P. aeruginosa cytochrome ᶜ551, the bulk of the work described in this thesis deals with the effect of pH on Em for a closely related cytochrome, Pseudomonas stutzeri 221 cytochrome ᶜ551. The P. stutzeri cytochrome shows a similar pattern of pH dependence of Em in that two pKs (pK₀ and pKᵣ) influence Em below pH9; however, pK₀ and pKᵣ occur nearly one pH unit higher (pK₀ = 7.6, pKᵣ = 8.3) than in P. aeruginosa cytochrome ᶜ551. Using high resolution ¹H NMR it was possible to show that haem propionic acid-7 ionises at pK = 7.6 in P. stutzeri ferricytochrome ᶜ551 and also that a histidine residue, His47, is deprotonated with pK = 7.6 in the ferricytochrome and pK = 8.3 in the ferrocytochrome. The pK of propionic acid-7 in the ferrocytochrome could not be measured by NMR and so it was not possible to demonstrate directly that its pK is redox state dependent. However, by chemically modifying His47 with ethoxyformic anhydride, which prevents the histidine from ionising between pH5 and 9, it was shown that the redox potential of P. stutzeri cytochrome was still pH dependent, implying that the redox state dependent ionisation of propionic acid-7 must indeed contribute to the fall in Em at alkaline pH. Since propionic acid-7 and His47 appear to ionise with exactly the same values of pK₀ and pKᵣ in the unmodified cytochrome, and since the propionic acid pKs are lowered by nearly 2 pH units upon modification of His47 with ethoxyformic anhydride, it was deduced that the two groups must interact with each other in a manner that raises the pKs of both species and allows their conjoint ionisation. A hydrogen bonding scheme is proposed in which propionic acid-7 and His47 both exist in a partially charged state at low pH.It was predicted that propionic acid-7 will ionise with redox state dependent pKs in all other cytochromes ᶜ551, and that the nature of the amino acid at sequence position 47 will be important in determining the values of pK₀ and pKᵣ. In this respect it was shown that P. stutzeri 224 and P. mendocina cytochromes ᶜ551, which both contain histidine at sequence position 47, have similar Em versus pH curves and pKᵣ/pKᵣ values to the P. stutzeri 221 cytochrome. NMR data for P. mendocina cytochrome ᶜ551 confirmed that propionic acid-7, and His47, ionise in this cytochrome also. However, P. denitrificans and Azotobacter vinelandii cytochromes ᶜ551 show only very slight pH dependence of redox potential below pH9 (i.e. pK₀ and pKᵣ very close together), a pattern which was not predictable in either case simply from consideration of the identity of the amino acid occurring at position 47 in the sequence.The Em versus pH curve was also obtained for Chlorobium thiosulphatophilum cytochrome ᶜ551, a cytochrome which is distantly related in sequence to the cytochromes ᶜ551. The general shape of the curve is similar to that observed for the cytochromes ᶜ551, with pK₀ = 6.3 and pKᵣ = 7.1. NMR data showed that a histidine residue is deprotonated with these pKs; this histidine may be sequentially analogous to His47 of P. stutzeri and P. mendocina cytochromes ᶜ551. The NMR data also suggested that a propionic acid substituent ionises. Thus the redox potential of cytochrome ᶜ555 appears to be affected by the same mechanism as in P. stutzeri and P. mendocina cytochromes ᶜ551, despite their diverse origins

Sustainability through a better system of regional planning: the CHRRUPP project

A pilot regional resource use planning project, called the Central Highlands Regional Resource Use Planning Project (CHRRUPP), is being undertaken in the rangelands of Queensland. CHRRUPP seeks to establish and to evaluate a more negotiated and integrated approach to regional planning for sustainable resource use. As a three-year research project, CHRRUPP is nearing completion: as an ongoing systems approach to regional planning, it is gradually moving to full community control

Sustainability through a better system of regional planning: the CHRRUPP project

A pilot regional resource use planning project, called the Central Highlands Regional Resource Use Planning Project (CHRRUPP), is being undertaken in the rangelands of Queensland. CHRRUPP seeks to establish and to evaluate a more negotiated and integrated approach to regional planning for sustainable resource use. As a three-year research project, CHRRUPP is nearing completion: as an ongoing systems approach to regional planning, it is gradually moving to full community control

Structure and Property Correlations in Heavy Atom Radicals

Neutral radicals represent versatile building blocks for the design of new conductive and magnetic molecular materials. In order to obtain good electron transport, materials displaying a high bandwidth W and a low on-site Coulomb repulsion energy U must be generated, and to this end, the pyridine-bridged bisdithiazolyl radicals were developed. As a result of resonance stabilization, these materials possessed a low U, a high thermal stability, and did not dimerize in the solid state. Unfortunately, their crystal structures consisted of slipped π-stack arrays that limited overall bandwidth and afforded Mott insulating ground states. To improve on these systems, two strategies were employed to increase orbital overlap between radicals. The first approach involved the removal of one of the R groups to allow for more superimposed π-stacking in the solid state. Although the desired packing motif was achieved for one derivative, and higher conductivity was observed, a subtle distortion along the π-stacks at low temperature resulted in diamagnetic behaviour, demonstrating the need for steric protection in preventing spin-quenching association in these compounds. The second strategy to improve W was to incorporate the heavier, more spatially diffuse selenium atom into the framework. Three selenium-containing isomers were developed and it was found that conductivity increased with selenium content, with room temperature values reaching 0.001 S/cm. For some derivatives σ-dimerization through the selenium atom is observed, and these compounds exhibited a dramatic response to applied pressure, with conductivity values increasing by 5 orders of magnitude under 5 GPa of pressure. When dimerization is avoided, isomorphous mapping of sulfur for selenium is generally achieved, although for one series of radicals, two space groups were obtained. For this family of compounds the effects of the crystal structure on the transport properties were examined. A series of EHT bandwidth calculations and DFT magnetic exchange energy calculations on a model 1D π-stack of radicals revealed that the experimental properties (both conductivity and magnetism) correlate well to theory, suggesting that the behaviour of these compounds can be predicted based on crystal structure, and that the design of compounds with specific properties may soon be possible

Can the use of Cannibis (Hemp), when mixed with additives, be a suitable substitute to conventional building materials?

This research will determine if it is viable to cultivate and process hemp into a building material to be used in the construction industry of South Africa. The effect on the environment of manufacturing and using conventional materials will be compared the cultivation and production of hemp building materials. The general opinion of professionals and contractors will be determined regarding the use of hemp building materials in their design and also using such materials for construction. This research will establish if further training and education of using hemp building materials is necessary for skilled labour. Lastly, the current knowledge and research of hemp construction materials in South Africa will be verified, and which projects in South Africa are currently using such materials. The legalisation of cultivating this plant will be investigated.Thesis (BSc. (Hons)(Quantity Surveying)--University of Pretoria, 2009.ai201

Using consensus analysis to assess mental models about water use and management in the Crocodile River catchment, South Africa

The content, structure, and distribution of mental models can be elicited and measured using a variety of methods. In this article we explore a method for eliciting mental models within the context of water use and management in South Africa. This method is consensus analysis, a technique developed in cognitive anthropology. We used it to analyze qualitative data from semistructured interviews, pilesorts, and questionnaires to test quantitatively the degree of sharing and diversity of mental models within and across social groups. The consensus analysis method focused on comparing the mental models of two key stakeholder groups in the Crocodile River catchment in South Africa, i.e., conservationists and irrigators, to better understand the level of consensus between these groups. We specifically investigated the level of agreement regarding: (1) major water users of the Crocodile River, (2) causes of the current problems with flows in the river, (3) consequences of the river not flowing, and 4) priorities for future use. We discuss the results and examine the strengths and challenges of consensus analysis for eliciting and measuring mental models. We also evaluated the usefulness of this method in assisting natural resource managers to identify strategies for improving integrated management of water resources

Hepatic effects of tartrazine (E 102) after systemic exposure are independent of oestrogen receptor interactions in the mouse

Tartrazine is a food colour that activates the transcriptional function of the human oestrogen receptor alpha in an in vitro cell model. Since oestrogens are cholestatic, we hypothesised tartrazine will cause periportal injury to the liver in vivo. To test this hypothesis, tartrazine was initially administered systemically to mice resulting in a periportal recruitment of inflammatory cells, increased serum alkaline phosphatase activity and mild periportal fibrosis. To determine whether an oestrogenic effect may be a key event in this response, tartrazine, sulphonated metabolites and a food additive contaminant were screened for their ability to interact with murine oestrogen receptors. In all cases, there were no interactions as agonists or antagonists and further, no oestrogenicity was observed with tartrazine in an in vivo uterine growth assay. To examine the relevance of the hepatic effects of tartrazine to its use as a food additive, tartrazine was orally administered to transgenic NF-κB-Luc mice. Pre- and concurrent oral treatment with alcohol was incorporated given its potential to promote gut permeability and hepatic inflammation. Tartrazine alone induced NF- κB activities in the colon and liver but there was no periportal recruitment of inflammatory cells or fibrosis. Tartrazine, its sulphonated metabolites and the contaminant inhibited sulphotransferase activities in murine hepatic S9 extracts. Given the role of sulfotransferases in bile acid excretion, the initiating event giving rise to periportal inflammation and subsequent hepatic pathology through systemic tartrazine exposure is therefore potentially associated an inhibition of bile acid sulphation and excretion and not on oestrogen receptor-mediated transcriptional function. However, these effects were restricted to systemic exposures to tartrazine and did not occur to any significant effect after oral exposure

The limited utility of electrocardiography variables used to predict arrhythmia in psychotropic drug overdose

OBJECTIVE: The aim of the present study was to examine the relationship between serious arrhythmias in patients with psychotropic drug overdose and electrocardiography (ECG) findings that have been suggested previously to predict this complication. METHODS: Thirty-nine patients with serious arrhythmias (ventricular tachycardia, supraventricular tachycardia or cardiac arrest) after tricyclic antidepressant overdose or thioridazine overdose were compared with 117 controls with clinically significant overdose matched to each case for the drug ingested. These patients with psychotropic drug overdose had presented for treatment to the Department of Clinical Toxicology, Newcastle and to the Princess Alexandra Hospital, Brisbane. The heart rate, the QRS width, the QTc and QT intervals, the QT dispersion, and the R wave and R/S ratios in aVR on the initial ECGs were compared in cases and controls. RESULTS: The cases had taken dothiepin (16 patients), doxepin (six patients), thioridazine (five patients), amitriptyline (five patients), nortriptyline (three patients), imipramine (one patient) and a combination of dothiepin and thioridazine (three patients). In 20 of the 39 patients with arrhythmias, the arrhythmia had been a presumed ventricular tachycardia. Of the other 19 patients, 15 patients had a supraventricular tachycardia, two patients had cardiac arrests (one asystole, one without ECG monitoring) and two patients had insufficient data recorded to make classification of the arrhythmias possible. The QRS was ≥ 100 ms in 82% of cases but also in 76% of controls. QRS ≥ 160 ms had a sensitivity of only 13% and occurred in 2% of controls. QRS > 120 ms, QTc > 500 and the R/S ratio in aVR appeared to have a stronger association with the occurrence of arrhythmia: QRS > 120 ms (odds ratio [OR], 3.56; 95% confidence interval [CI], 1.46–8.68), QTc > 500 (OR, 3.07; 95% CI, 1.33–7.07), and R/S ratio in aVR > 0.7 (OR, 16; 95% CI, 3.47–74). Excluding thioridazine overdoses and performing the analysis for tricyclic antidepressant overdoses alone gave increased odds ratios for QRS > 120 ms (OR, 4.83; 95% CI, 1.73–13.5) and QTc > 500 (OR, 4.5; 95% CI, 1.56–13) but had little effect on that for the R/S ratio in aVR > 0.7 (OR, 14.5; 95% CI, 3.10–68). CONCLUSION: ECG measurements were generally weakly related to the occurrence of arrhythmia and should not be used as the sole criteria for risk assessment in tricyclic antidepressant overdose. The frequently recommended practice of using either QRS ≥ 100 ms or QRS ≥ 160 ms to predict arrhythmias is not supported by our study. R/S ratio in aVR > 0.7 was most strongly related to arrhythmia but had estimated positive and negative predictive values of only 41% and 95%, respectively. The use of these specific predictors in other drug overdoses is not recommended without specific studies

Influence of Surgical Technique on Mastectomy and Reexcision Rates in Breast-Conserving Therapy for Cancer

Introduction. Breast conserving surgery (BCS) requires tumor excision with negative margins. Reexcision rates of 30–50% are reported. Ultrasound localization, intraoperative margin pathology, and specimen mammography have reduced reexcisions, but require new equipment. Cavity shave margin (CSM) is a technique, utilizing existing equipment, that potentially reduces reexcision. This study evaluates CSM reexcision impact. Methods. 522 cancers treated with BCS were reviewed. Patients underwent standard partial mastectomy (SPM) or CSM. Data collected included demographics, pathology, and treatments. Results. 455 SPMs were compared to 67 CSMs. Analysis revealed no differences in pathology, intraductal component, or neoadjuvant chemotherapy. Overall reexcision rate = 43%. Most reexcisions were performed for DCIS at margin. SPMs underwent 213 reexcisions (46.8%), versus 16/67 (23.9%) CSMs (P = 0.0003). Total mastectomy as definitive procedure was performed after more SPMs (P = 0.009). Multivariate analysis revealed CSM, % DCIS, tumor size, and race to influence reexcisions. Conclusions. CSM is a technique that reduces reexcisions and mastectomy rates