Showing papers by "University of Leicester published in 1977"

Properties of the Penicillin-Binding Proteins of Escherichia coli K12

Abstract: Benzyl[14C]penicillin binds to six proteins with molecular weights between 40000 and 91000 in the inner membrane of Escherichia coli. Two additional binding proteins with molecular weights of 29000 and 32000 were sometimes detected. All proteins were accessible to benzyl[14C]penicillin in whole cells. Proteins 5 and 6 released bound benzyl[14C]penicillin with half times of 5 and 19 min at 30 degrees C but the other binding proteins showed less than 50% release during a 60-min period at 30 degrees C. The rate of release of bound penicillin from some of the proteins was greatly stimulated by 2-mercaptoethanol and neutral hydroxylamine. Release of benzyl[14C]penicillin did not occur if the binding proteins were denatured in anionic detergent and so was probably enzymic. No additional binding proteins were detected with two [14C]cephalosporins. These beta-lactams bound to either all or some of those proteins to which benzyl[14C]penicillin bound. No binding proteins have been detected in the outer membrane of E coli with any beta-[14C]lactam. The binding of a range of unlabelled penicillins and cephalosporins were studied by measuring their competition for the binding of benzyl[14C]penicillin to the six penicillin-binding proteins. These results, together with those obtained by direct binding experiments with beta-[14C]lactams, showed that penicillins bind to all six proteins but that at least some cephalosporins fail to bind, or bind very slowly, to proteins 2, 5 and 6, although they bind to the other proteins. Since these cephalosporins inhibited cell division and caused cell lysis at concentrations where we could detect no binding to proteins 2, 5 and 6, we believe that these latter proteins are not the target at which beta-lactams bind to elicit the above physiological responses. The binding properties of proteins 1, 3, and 4 correlate reasonably well with those expected for the above killing targets.

A neutron diffraction study of hydration effects in aqueous solutions

Abstract: The nature of ionic hydration for the cations in NiCl2 solution and the anions in NaCl solution has been investigated by neutron diffraction experiments on samples which have been isotropically enriched. Well defined hydration numbers are found for both the Ni2+ ion and Cl- ion.

Temperature-Sensitive Cell Division Mutants of Escherichia coli with Thermolabile Penicillin-Binding Proteins

Abstract: The thermostability of the penicillin-binding proteins (PBPs) of 31 temperature-sensitive cell division mutants of Escherichia coli has been examined. Two independent cell division mutants have been found that have highly thermolabile PBP3. Binding of [14C]benzylpenicillin to PBP3 (measured in envelopes prepared from cells grown at the permissive temperature) was about 30% of the normal level at 30°C, and the ability to bind [14C]benzylpenicillin was rapidly lost on incubation at 42°C. The other PBPs were normal in both mutants. At 30°C both mutants were slightly longer than their parents and on shifting to 42°C they ceased dividing, but cell mass and deoxyribonucleic acid synthesis continued and long filaments were formed. At 42°C division slowly recommenced, but at 44°C this did not occur. The inhibition of division at 42°C was suppressed by 0.35 M sucrose, and in one of the mutants it was partially suppressed by 10 mM MgCl2. PBP3 was not stabilized in vitro at 42°C by these concentrations of sucrose or MgCl2. Revertants that grew as normal rods at 42°C regained both the normal level and the normal thermostability of PBP3. The results provide extremely strong evidence that the inactivation of PBP3 at 42°C in the mutants is the cause of the inhibition of cell division at this temperature and identify PBP3 as an essential component of the process of cell division in E. coli. It is the inactivation of this protein by penicillins and cephalosporins that results in the inhibition of division characteristic of low concentrations of many of these antibiotics.

Indomethacin--a calcium antagonist.

Abstract: The mechanism by which indomethacin inhibits inflammation is still uncertain. Many different pharmacological actions of indomethacin have been described, most of which have been invoked at one time or another as an explanation for the observed anti-inflammatory properties of the drug. Extensive general reviews of this subject have appeared (Domenjoz, 1966; Smith & Dawkins, 1971). The present review, therefore, will be confned to one particular property of indomethacin which has received little attention in the past, namely the ability of indomethacin to interfere with the participation of calcium ions in biological processes. 1.

Cs(+) causes a voltage-dependent block of inward K currents in resting skeletal muscle fibres.

Abstract: WHEN frog skeletal muscle fibres are bathed in solutions containing Cs+ and K+ in the ratio 1 : 4,000, a reduction is observed in the size of inward K currents through the resting membrane. This effect is enhanced by an increase in either hyperpolarisation or external Cs+ concentration. It can be predicted from these findings that regenerative changes in membrane potential should be obtainable in fibres, in the presence of Cs+, that are hyperpolarised by means of a current electrode. Such responses are described in the last part of this report. In squid axon and frog node1,2, internal Cs+ produces a voltage-dependent block of the delayed, outward K currents, though the ratio of Cs+ to K+ required for this effect is far greater than that used in the experiments reported here. A closer parallel can be drawn between our findings and those recently reported on the inward K currents in the starfish egg cell3.

The concentration dependence of transport processes: A general description applicable to the sedimentation, translational diffusion, and viscosity coefficients of macromolecular solutes

Abstract: The transport coefficients of macromolecular solutes are normally extrapolated to “infinite dilution” to remove the effects of concentration-dependence terms, for which no satisfactory general treatment has been available. It is shown that a simple general treatment for the concentration-dependence effect can be derived, applicable to limiting concentrations in the absence of charge effects or other forms of specific interactions between the solute particles. The relationships derived are of considerable practical significance for the characterization of the size and conformation of natural and synthetic polymers.

Binding of Thienamycin and Clavulanic Acid to the Penicillin-Binding Proteins of Escherichia coli K-12

Abstract: Thienamycin and clavulanic acid are new beta-lactam derivatives with structures markedly different from those of penicillins or cephalosporins. Both derivatives had the same general mode of action as typical beta-lactam antibiotics since they bound to precisely the same proteins as [(14)C]benzylpenicillin. Thienamycin showed high affinity for penicillin-binding proteins 1, 2, 4, 5, and 6 and a lower affinity for protein 3. Protein 2 had the highest affinity for thienamycin, and concentrations from the minimal morphological change concentration (0.1 mug/ml) up to about 0.6 mug/ml resulted in the conversion of Escherichia coli KN126 into large osmotically stable round cells. Above a concentration of 0.6 mug/ml, rapid cell lysis occurred with the release of the cell contents as spheroplasts. Clavulanic acid showed good affinity for penicillin-binding protein 2, moderate affinity for proteins 1, 4, 5, and 6, and low affinity for protein 3. Protein 2 had the highest affinity for clavulanic acid, and concentrations from the minimal morphological change concentration (30 mug/ml) up to about 50 mug/ml produced a mixture of slightly elongated, swollen, bulging, and lemon-shaped cells. Above a concentration of 50 mug/ml, rapid lysis occurred with production of spheroplasts. The properties of thienamycin and clavulanic acid were compared with those of the penicillins, cephalosporins, and amidinopenicillanic acids.

The electronic structure of lithium‐based liquid semiconducting alloys

Abstract: The resistivity, ρ, and the thermoelectric power, S, for liquid lithium alloys of the type Li x M1-x where 0

Dust clouds and frictional generation of glow discharges on Mars

Abstract: A REMARKABLE characteristic of those samples of the martian soil which have so far been analysed is the absence of carbonaceous matter down to the parts per billion (109) level1. As well as a lack of endogenous organic material there is no sign of the component expected from infalling carbonaceous meteorites. The inorganic particles constituting the fine martian soil seem to be extremely ‘clean’—far cleaner than terrestrial desert or Antarctic analogues. I suggest here that glow discharges generated by friction within dust clouds might explain this apparent absence of carbonaceous matter. In addition glow discharges might account for some reactions noted in the Viking biological experiments.

A method for testing the distinctness of clusters: A test of the disjunction of two clusters in Euclidean space as measured by their overlap

Abstract: A method is described for testing the distinctness of two clusters in Euclidean space. One first calculates the projections, q,of the N1and N2members of the clusters onto the line joining the cluster centroids. From the distributions of qan index of disjunction, W,is calculated, which corresponds to an index of overlap, VG.The quantity W√(N1+N2)is distributed as noncentral tsubject to assumptions on the multivariate normal distribution of the clusters. This allows a test of whether the observed disjunction is significantly greater than a chosen figure, which is equivalent to testing whether the overlap of the clusters is significantly less than a corresponding value of VG.Two clusters that appear distinct may be produced simply by the partitioning of a homogeneous swarm into two contiguous regions. Provided that the clusters form a dichotomy in a dendrogram, and that the clustering method yields geometrically convex clusters, a conservative test of this situation can be derived by determining the excess of Wover the value expected for a rectangular distribution.

A calcium dependent inward current in frog skeletal muscle fibres

Abstract: Slow inward currents are here reported in frog skeletal muscle. The currents are turned on by depolarising the membrane beyound about −45 mV, and are blocked by replacement of Ca2+ by Mg2+ and in the presence of Ca2+ by Co2+ at 20mM.

X-ray photoelectron spectroscopy studies of polymer surfaces

Abstract: The effect of melting polyethylene on aluminium has been re-examined using X-ray photoelectron spectroscopy. Even at 150° C, low and high density polyethylenes show degrees of oxidation similar to that observed with conventional pretreatments; large increases in adhesion are also observed. The results are discussed in relation to transcrystalline regions and weak boundary layers.

Patterns of silver staining of human chromosomes

Abstract: The chromosomes of twenty individuals with normal karyotypes were studied to determine the patterns of staining with the Ag-AS technique. These patterns were shown to be variable from one individual to another, but characteristic and constant within each individual. In addition, one patient with chronic lymphocytic leukemia was studied, and shown to have an Ag-AS staining pattern that was distinctly different from that of normal subjects.

Quenching of chlorophyll fluorescence by β-carotene

Abstract: CAROTENOID pigments are closely associated with chlorophyll molecules in the chloroplast structure1,2. Some carotenoids, for example fucoxanthol3, can act as efficient sensitisers for the formation of the excited singlet state of chlorophyll although others, such as β-carotene, are very inefficient2,4,5. Other functions of carotenoids include acting as a deactivator of triplet chlorophyll (and hence protect the chlorophyll from photodegradation and also intercept the production of singlet oxygen) and as a deactivator of singlet oxygen6. Here we report in vitro experiments which unequivocally demonstrate that β-carotene quenches the excited singlet state of chlorophyll.

Freeze Preservation of Cultured Plant Cells. III. The Pregrowth Phase

Abstract: There is an inverse relationship between cell size and capacity to survive the freeze-preservation protocol. Pregrowth of cell suspensions in media rendered more negative in water potential by addition of mannitol enhances the survival capacity of Acer pseudoplatanus and Capsicum annuum cells but this effect can only partially be explained in terms of the associated reduction in mean cell size. Studies with cell suspensions of Daucus carota indicate the importance for successful freeze-preservation of the stage in the growth cycle of suspensions propagated in batch culture; highest survival was recorded for cells taken at lag phase or early exponential phase. Regrowth of recovered cells depends upon the establishment of an appropriate inoculum density of cells which have retained the capacity to divide. The dividing cells only achieve a growth rate equal to that of untreated cells after a number of cell generations. A proportion of the recovered cells giving an initial positive fluorescein diacetate reaction lose this capacity rapidly (within 24 h), others lose the capacity more slowly and others, in which the positive reaction persists, are incapable of division. These observations indicate that different levels of injury are inflicted by the freeze-preservation protocol and that only in a proportion of the cells is the injury reparable or compatible with growth by cell division.

What is going on in lichen planus

Abstract: The classical histopathological features of lichen planus were first clearly described nearly 70 years ago (Darier, 1909). They are instantly recognizable, thus giving the impression that a special pathogenesis could well be implicated in the aetiology of lichen planus. At present we still have a lot to learn, and perhaps more important to explain, in beginning to understand the pathogenesis of lichenoid tissue reactions. The aim of this symposium was to explore recent developments which have been taking place in trying to ellucidate the pathogenesis of lichenoid tissue reactions using lichen planus as the prototype. Recent texts (Pinkus, 1973) define lichenoid tissue reactions as those exhibiting epidermal basal cell damage as the primary event, which then initiates the cascade of changes which we see and recognize in the fully developed lichen planus histopathology. However, it is worth remembering that earlier, there had been considerable controversy as to whether lichen planus was primarily a dermal disease (Sabouraud, 1910), or whether the changes were initiated in the epidermis (Kyrle, 1925). In a classic paper, Thyresson & Moberger (1957) produced the first really convincing evidence that degenerating basal epidermal cells became colloid bodies and that this occurred very early in the pathological process. Thyresson & Moberger postulated that degeneration of epidermal basal cells was the primary event which they attributed to a virus infection. A viral aetiology (Thyresson & Moberger, 1957; Swanbeck & Thyresson, 1964) has always been an attractive theory and has been used to explain the induction of lichen planus by experimental scratching (Stankler & Ewen, 1974). However, numerous electron microscopic or virus isolation studies have failed to provide convincing proof that lichen planus is induced by a virus infection (e.g. Fry & Withers, 1968; Sarkany & Gaylarde, 1970)If progress towards a possible viral hypothesis has been disappointingly inconclusive, we do now have a much clearer understanding of the structure of the colloid bodies (see Ebner & Gebhart, 1975, 1976). The differentiation of degenerating epidermal cells into fibrillar or dyskeratotic types is discussed fully by Walter Gebhart in the next article (Ebner & Gebhart, 1977). The remainder of this manuscript reviews epidermal cell proliferation, enzyme histochemical and immunological aspects of lichen planus.

Blood Pressure Response of Nephrectomized Hypertensive Rats to Converting Enzyme Inhibition: Evidence for Persistent Vascular Renin Activity

Abstract: 1. Blood pressure and plasma renin activity were studied after bilateral nephrectomy in groups of rats with hypertension caused by unilateral renal ischaemia with the opposite kidney left intact. 2. Although blood pressure showed only a small fall in the first hour after bilateral nephrectomy, plasma renin activity fell rapidly with a half-life of 10 min. 3. Infusion of converting enzyme inhibitor (SQ20881) produced a 26·1% fall in blood pressure 1 h after nephrectomy, 24·0% at 2 h and 4·6% at 6 h. 4. An angiotensin antagonist (Sar1-Ala8-angiotensin II) was infused into hypertensive rats 1 h after nephrectomy; this blocked the vasodepressor action of the converting enzyme inhibitor, indicating that the fall in blood pressure produced by the inhibitor was due to its action upon the renin-angiotensin system. 5. The renin—angiotensin system maintains blood pressure in this model even after plasma renin has fallen to insignificant levels. This supports the view that vascular renin activity has a longer half-life than circulating renin and is important in the control of blood pressure.

Plaque Removal by the Bass and Roll Brushing Techniques

Abstract: The effectiveness of plaque removal using two brushes with the Bass technique and two with the Roll method was compared in a group of 38 junior dental students using a crossover experimental design. The Bass technique was superior to the Roll method in cleaning the tooth tissue adjacent to the gingival tissue on the lingual and facial aspects, but no significant differences were found in the overall effectiveness. Cleaning of all tooth surfaces was at an unacceptable level and it is concluded that efficient tooth cleaning is not achieved by detailed instruction at a single visit including a demonstration of competence by the subject and the issue of written instructions. Repetition of the instruction within 3 weeks did not achieve a higher standard of plaque removal.

The variation in the information content of titles of research papers with time and discipline

Abstract: The relative information content of titles of research papers in different subject areas has been examined by counting the number of their ‘substantive’ words in eleven English periodicals, two French and two German. Chemistry and botany (in which KWIC indexes are already produced) are found to have the highest values, followed by physics, medicine, history, and the social sciences, with philosophy lowest. The information content of the foreign titles when translated into English was almost equal to that of English titles in the same subjects. Most subjects showed a significant increase in the number of substantive words between 1947 and 1973. Some difficulties of searching by title due to the vocabularies of non‐scientific subjects are discussed.

Feynman propagator in curved space-time

Abstract: The Wick rotation is generalized in a covariant manner so as to apply to curved manifolds in a way that is independent of the analytic properties of the manifold This enables us to show that various methods for defining a Feynman propagator to be found in the literature are equivalent where they are applicable We are also able to discuss the relation between certain regularization methods that have been employed

Effect of indomethacin and related drugs on the calcium ion-dependent secretion of lysosomal and other enzymes by neutrophil polymorphonuclear leucocytes in vitro.

Abstract: 1 Rabbit isolated peritoneal neutrophil polymorphonuclear leucocytes were depleted of calcium by exposure for 1 h to calcium-free bathing fluid at 4 degrees C. 2 Addition of calcium ions to the previously calcium-depleted calls during incubation at 37 degrees C stimulated the release of beta-glucuronidase and of lysozyme but not of lactate dehydrogenase. 3 Low concentrations of indomethacin, flufenamate or salicylate, such as those which occur in the blood plasma after therapeutic doses of these drugs, selectively inhibited the calcium-induced release of beta-glucuronidase. The slight release of this enzyme which occurred in the absence of added calcium ions was not altered by these drugs, neither was the release of lactate dehydrogenase. 4 Release of lysozyme was inhibited by low concentrations of salicylate, amidopyrine or oxyphenbutazone, independent of the presence or absence of calcium ions. 5 Chloroquine, hydrocortisone or colchicine did not alter the release of leucocyte enzymes.

Oxygen Consumption of the Terrestrial Mite Alaskozetes Antarcticus (Acari: Cryptostigmata)

Abstract: Analysis of 148 measurements of individual respiration rate showed that although respiration was linearly related to live weight on a double log 10 scale, there were significant differences between rates at 0°, + 50° and +10 °C Proto- and deutonymphal metabolic rates were higher than other stages, especially at +10 °C Q 10 values ranged from 207 to 383 over 0° to +10 °C Equations relating individual respiratory rate to live weight and temperature for A antarcticus , and metabolic rate to temperature for 10 species of Antarctic terrestrial invertebrates were developed Comparison with temperate data indicated considerable cold adaptation in the Antarctic species with 3–5 times increased metabolism It was calculated that 78–82 % of the energy assimilated may be used in respiration by A antarcticus