Biomedical subjects
K E Taylor
Publications and source records attributed to K E Taylor.
Inactivation of horseradish peroxidase by phenol and hydrogen peroxide: a kinetic investigation.
Inactivation of horseradish peroxidase (HRP) was examined in the presence of hydrogen peroxide alone and in the presence of hydrogen peroxide plus phenol. HRP is inactivated upon exposure to hydrogen peroxide (H2O2) by the combination of two possible pathways, dependent upon hydrogen peroxide concentration. At low H2O2 concentrations (below 1.0 mM in the absence of phenol), inactivation is predominantly reversible, resulting from the formation and accumulation of catalytically inert intermediate compound III. As H2O2 concentrations increase, an irreversible mechanism-based inactivation process becomes predominant. The overall inactivation comprised of both processes exhibits a second-order inactivation rate constant (kapp) of 0.023 +/- 0.005 M-1 s-1 at pH 7.4 and 25 degrees C. In the presence of both hydrogen peroxide fixed at 0.5 mM and phenol, HRP was inactivated in an irreversible, time- and phenol concentration-dependent process, also mechanism-based, with a kapp of 0.019 +/- 0.004 M-1 s-1.
Enzymatic removal of selected aromatic contaminants from wastewater by a fungal peroxidase from Coprinus macrorhizus in batch reactors.
The use of enzymes such as horseradish peroxidase (HRP) for degrading or removing toxic organics from synthetic wastewater has been demonstrated previously. Potential alternatives to HRP are other peroxidases, various ligninases, haloperoxidases and laccases. Results of this study indicate that a fungal peroxidase from Coprinus macrorhizus (CMP) has the capability to catalyze the same reactions as HRP. Similarly, in batch reactors the trend and removal efficiency of aromatic compounds by CMP from synthetic wastewater depend on the nature of the compound.
The effects of the metabotropic glutamate receptor agonist 1S,3R-ACPD on neurones in the rat primary somatosensory cortex in vivo.
The selective glutamate metabotropic receptor agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) was applied iontophoretically to cells in the rat primary somatosensory cortex (SI) in vivo. In contrast to other in vivo studies, distinct excitatory and depressant effects were observed. The excitatory responses could not be blocked by ionotropic antagonists, as evidence that they were mediated by a metabotropic receptor. The depressant effects were most pronounced on natural synaptic transmission, suggesting that a presynaptic receptor may be involved, although responses to iontophoretically applied agonists were also affected. Comparison with the presumed presynaptic glutamate receptor agonist L-2-amino-4-phosphonobutyrate (L-AP4) suggest that the depressant effects of 1S,3R-ACPD could be partially mediated by a presynaptic autoreceptor.
Identity and coping with mental illness in long-stay psychiatric rehabilitation.
The literature on coping with mental illness is reviewed. A study is reported which was designed to operationalize and measure the responses to chronic psychiatric illness of denial or adoption of a sick role outlined by Wing & Morris (1981) and Shepherd (1984) and to investigate their correlates and relationship to identity as measured by Thompson (1988). On the basis of existing literature, it was anticipated that subjects who identified themselves as 'community members' would tend to cope by denial of psychiatric problems whilst those seeing themselves as a 'typical psychiatric patient' would exaggerate their disabilities. Although both types of response and identity were found within the group studied, this prediction was not confirmed: responses of patients to their illness were independent of identity, and had different sets of correlates. As compared with 'exaggerators', 'deniers', tended to have social networks within the hospital, and showed higher self-esteem and less subjective distress. Community identity, on the other hand, was related to actually going into the community, better overall functioning (especially in the areas of social activities and community skills), and poorer compliance with medication. The theoretical and practical implications of these findings are discussed.
Transfer of long-stay psychiatric patients: a preliminary report of inter-institutional relocation.
A large mental hospital closed in November 1986. Twenty-eight female patients formed the first group to be transferred to a second psychiatric hospital. Patients in the receiving hospital were identified as controls. Both transfer and control groups were studied before the move and at six- and 12-month follow-ups. No differences in mortality or morbidity were found between groups, but the transferred patients increased in behavioural dependency. Within the transfer group, patients became more positive towards the move over time. Results are discussed with reference to previous studies of relocation effects on elderly people.
Partner support and the use of coping techniques in labour.
This study examined the relationship between partner support, use of pain control techniques and epidural anaesthesia in 80 primiparous women. It was found that the use of psychological 'pain control' techniques did not reduce the intensity of labour pain, nor did their use enable women to do without an epidural anaesthesic. However, the use of techniques did correlate with reduced frequency of anaesthesia when women were consistently supported and encouraged throughout labour, and when the labour was relatively short.
A test of a common assumption regarding the use of antenatal training during labour.
The nature and purpose of antenatal classes are reviewed briefly, together with the common assumption that women given antenatal training to cope with their labour pains do all in fact make use of the breathing and postural techniques which have been taught in the classes when they come to labour itself. This assumption was tested by obtaining reports of the use of such techniques from sixty primiparous mothers after their labours. The results showed that the majority of these women did use their coping techniques at the onset of contractions, but as labour progressed toward delivery fewer and fewer mothers did so, less than a third practising any kind of coping techniques by the time they were in the second stage of labour. Of the more than two thirds remaining, a very substantial number could be accounted for by the mothers who had epidural analgesia, but, even allowing for this, more than half of the 'non-epidural' mothers failed to make use of their postural and breathing techniques during the second stage of labour. These findings suggest that it should no longer be assumed that all women taught to cope with labour pains by learning postural and breathing techniques in antenatal classes will necessarily be able to use them throughout labour itself.
A new peroxidase color reaction: oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone (MBTH) with its formaldehyde azine. Application to glucose and choline oxidases.
Hydrogen peroxide in the presence of horseradish peroxidase effects the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with its formaldehyde azine to form a tetraazapentamethine dye. The blue chromophore, when formed at pH 3.5 and quenched with acetone or 1 N hydrochloric acid, has an extinction coefficient of 69 +/- 2 or 55 +/- 2 mM-1 cm-1, respectively. This chromogen system has been adapted for enzymatic determinations of hydrogen peroxide and of glucose in the 10- to 45-nmol range and of choline in the 5- to 20-nmol range.
Polyarthritis associated with breast carcinoma.
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Effects of pH and sulfhydryl specific reagents on 4-fumarylacetoacetate fumarylhydrolase.
The pH-dependence of fumarylacetoacetase (4-fumarylacetoacetate fumaryl-hydrolase, EC 3.7.1.2) activity was studied in the pH range 6.25-8.50. After correction of the substrate concentration for enolate formation, the Michealis constant was found to be pH independent in this range. Likewise, the Ki values for the competitive inhibitors chloride and fluoride were found to be independent of pH between 6.25-8.50. A bell-shaped curve described the log V vs. pH dependence, and ionization constants of 6.5 and 8.2 were calculated. Tentatively an imidazole group and a sulfhydryl group were assigned to the constants 6.5 and 8.2, respectively. Both p-hydroxymercuribenzoate and 5,5'-dithiobis(2-nitrobenzoic acid) react with both sulfhydryl groups per subunit in the native protein and three sulfhydryl groups per subunit in the denatured protein. Substrate protects one sulfhydryl group in the native protein from reaction with 5,5'-dithiobis(2-nitrobenzoid acid). Substrate or the competitive inhibitor, fluoride, protect the enzyme from inactivation by p-hydroxymercuribenzoate. In addition p-hydroxymercuribenzoate shows saturation kinetics. Neither sulfhydryl inhibitor completely inactivates the enzyme. The enzyme is described as having three sulfhydryl groups per subunit, one of which is inaccessible to the sulfhydryl specific reagents when the protein is in the native state. One of the two accessible sulfhydryl groups is either near the active site or essential in maintaining the structure of the protein.
Role of dose interval in the acquisition of tolerance to methylphenidate.
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Effect of hypotension on atherogenesis and aortic wall composition.
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Differential effects of methylphenidate on signalled and non-signalled reinforcement.
Rats were trained to press a bar with water reinforcement under a variable interval 15-sec (VI 15), variable interval 15-sec signalled-reinforcement (VI SD), or a differential-reinforcement-of-low-rate 10-sec (DRL 10) schedule. Methylphenidate (MP) had little effect on response rates or reinforcements-earned in the VI 15 group. However, MP increased response rates in a dose-related manner in the VI SD and the DRL 10 groups. These findings and additional results reported in the literature suggest that signalled reinforcement does not necessarily antagonize the rate-increasing effects of the amphetamine-type drugs.
Artery stenosis inhibits regression of diet-induced atherosclerosis.
Reduction of blood pressure and serum cholesterol levels is associated with reduced risk for the development of arteriosclerotic disease. Experimental studies indicate that reduced cholesterol levels result in arrest or regression of established diet-induced arterial lesions, but the effects of blood pressure reduction on such lesions are not clear. In order to investigate the effects of blood pressure on the regression of established lesions, we induced aortic intimal disease in cynomolgus monkeys by means of an artherogenic diet, produced midthoracic aortic coarctations, and restored the animals to low-cholesterol diets for 6 months. Diet control animals were neither coarctated nor restored to low-cholesterol diets. Animals with severe aortic stenosis and the regression diet had the same degree of abdominal aortic atherosclerosis and mural cholesterol content as diet control animals but esterified cholesterol and collagen content was elevated. Animals with mild coarctation and consuming the regression diet had significantly less abdominal aortic atherosclerosis than the diet control animals or the animals with severe coarctation. Although stenosis prevented the induction of lesions in previous experiments, the present study indicates that it did not reverse or delay progression of previously established lesions. The effect of pressure reduction on atherogenesis, even in the presence of reduced cholesterol levels, may depend on the extent and nature of the underlying lesions.
Endothelial integrity at aortic ostial flow dividers.
Previous investigators have examined the luninal surfaces of perfusion fixed rabbit aortas and reported endothelial damage about aortic ostial flow dividers. These changes have been considered to represent in vivo endothelial injury predisposing to atherosclerosis at these sites. Although standard pressure perfusion fixation techniques were used by these investigators, the fixed aortas were usually cut, bent open and pinned to flat surfaces before viewing. Such procedures distort the aortic media and could result in artifactual endothelial disruptions. We therefore studied the effect of post-fixation aortic manipulation on luminal surface morphology about aortic ostia. Rabbit aortas were fixed by perfusion in situ, while intra-aortic pressure was continuously monitored. When the aortas were opened by means of two parallel, lateral, longitudinal cuts, so that bending and pinning was avoided and normal vessel curvature was maintained, no endothelial disruption occurred about aortic ostia. When aortas were opened with one cut, bent open and pinned flat, ostial flow dividers were somewhat stretched and elongated and there was endothelial disruption in the form of spindle cell formation at the center portion of the flow dividers. Endothelial deformation due to bending during pinning probably occurs preferentially at the flow dividers because the media is thickest at this point. The greater deformability at the adjacent media and differences in compliance between media and intima results in stretching, bending and plication of the intima over the projecting flow divider. Studies attempting to relate endothelial changes to differences in shearing stress about ostia must take into account deformations introduced by post-fixation manipulation.
Dihydroxyacetone reductase from Mucor javanicus. 1. Isolation and properties.
An NADPH-dependent oxidoreductase has been extracted from the mycelium of the fungus Mucor Javanicus (Wehmer) and enriched 1000-fold with respect to the protein contained in the crude extract after centrifugation at 2600 X g. The molecular weight of the enzyme was estimated by gel filtration to be about 100 000; electrophoresis under dissociating conditions indicates four subunits of molecular weight about 28 000. Data on stability and activity of the enzyme as a function of pH and temperature are reported. From a kinetic study and product analysis of the reduction of the two enantiomeric trans-1-decalones and also from a kinetic study of the oxidation of the two diastereomeric pairs of trans-1-decalols it follows that the enzymes is an e-Si oxidoreductase (according to the nomenclature proposed by Dutler et al., Eur. J. Biochem. 22 [1971]203-212 and Prelog and Helmchen, Helv. Chim. Acta, 55 [1972] 2581-2598). This classification is amply confirmed by the kinetic behaviour of a large number of alicyclic substrates. Using (4-2HSi-labelled coenzyme to reduce (9S)-trans-1,4-decalindione, it was shown that the enzyme is HSi (= HS = HB)-stereospecific with respect to the coenzyme. It is demonstrated that the oxidoreductase from Mucor javanicus can be used for the preparation of optically pure chiral alcohols and ketones. In the following paper evidence is presented that the natural substrate of the enzyme is dihydroxyacetone.
Dihydroxyacetone reductase from Mucor javanicus. 2. identification of the physiological substrate and reactivity towards related compounds.
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