Showing papers by "University of Dundee published in 1975"

TRANSPORT OF INDOLEACETIC ACID IN PLANT CELLS IN RELATION TO pH AND ELECTRICAL POTENTIAL GRADIENTS, AND ITS SIGNIFICANCE FOR POLAR IAA TRANSPORT

Abstract: SUMMARY The distribution of IAA between the vacuole and the bathing solution in Hydrodictyon africanum is consistent with passive entry of undissociated IAA and passive efflux of both undissociated IAA and of IAA-, with PIAA (permeability coefficient)* about io-3 cms-1 and PIAA- about -6 -1A o-6 cm s . The involvement of IAA- in the efflux results from the inside-negative P.D. between the medium and the vacuole. The cytoplasm is at a higher pH than either the vacuole or the bathing solution used in most experiments; this is maintained by active H+ efflux at the plasmalemma, and active influx at the tonoplast. In this situation the efflux of IAA- is further promoted by the increased concentration of IAA- in the relatively alkaline cytoplasm. Thus the apparent active efflux of IAA from these cells can be explained in terms of passive driving forces of concentration and electrical potential acting on IAA and IAA-, with the distribution of these two species dictated ultimately by PIAA, PIAA-) the pH of the various compartments and the electrical potential difference between them. If PIAA/PIAA- were larger at the apical than at the basal end of coleoptile cells, such an effect could explain polar IAA transport, with metabolic energy being used only to maintain the relative permeabilities to the two species, the pH gradient and the electrical gradient.

An Ideal Penalty Function for Constrained Optimization

Abstract: This chapter presents an ideal penalty function for constrained optimization. The penalty function is used in the usual way, that is, for any given value of the parameters , S , a vector , ( S ) is obtained that minimizes ϕ( , , S ) without constraints. There is an outer iteration in which and S are changed so as to cause the solutions , ( , S ) → *. A well-known penalty function is one with = 0, in which case this convergence is ensured by letting σ i → ∞, i = 1, 2, …, m . The chapter presents some optimality results for Lagrange multipliers, which show that the optimum choice of the (or ) parameters for the Powell/Hestenes/Rockafellar penalty function is determined by a maximization problem in terms of these parameters.

The Hormonal Control of Activity of Skeletal Muscle Phosphorylase Kinase

Abstract: Two tryptic phosphopeptides containing the sites on the α and β subunits of phosphorylase kinase which are phosphorylated by protein kinase, dependent on adenosine 3′: 5′-monophosphate (cyclic AMP), have been isolated and their amino acid sequences have been determined. 32P-labelled phosphorylase kinase, containing 1.9 mol phosphate per mol enzyme, was digested with an equimolar quantity of trypsin for 2.5 min at pH 7.0, 20°C. This treatment released nearly all the 32P radioactivity associated with the β subunit as trichloroacetic-acid-soluble material. Only a small proportion of the 32P radioactivity associated with the α subunit was solubilised, the remainder being removed in the trichloroacetic acid pellet. The β-subunit tryptic phosphopeptide was completely resolved from traces of the α-subunit phosphopeptide by gel filtration on Sephadex G-25. Further purification by peptide mapping separated the phosphopeptide into four components, each derived from the same nine-amino-acid segment of the βchain, which was found to possess the sequence:Gln-Ser-Gly-Ser(P)-Val−IleTyr-Pro-Leu-Lys. The four components were produced by the partial cyclisation of the N-terminal glutaminyl residue, and by the presence of two alleles for the β subunit in the rabbit population, which led to a valine-isoleucine ambiguity. The α-subunit phosphopeptide was liberated from the trichloroacetic acid pellet by redigestion with trypsin. It was the largest component in the digest which remained soluble in 5% trichloroacetic acid, and obtained in a highly purified form by a single filtration on Sephadex G-50. The peptide comprised 39 amino acids of which nine were serine and three were threonine residues. Only one residue, the serine at position three from the amino terminus, was phosphorylated. The amino-terminal sequence of the peptide was shown to be: Arg-Leu-Ser(P)-Ile-Ser-Thr-Glu-Ser-Glx-Pro-Asx-Gly. The sequences confirm the stoichiometry of the reaction and the absolute specificity of cyclic-AMP-dependent protein kinase for just two of the 200 serine residues in the enzyme. These results and an inspection of the rate of phosphorylation of a number of skeletal muscle proteins, including each enzyme of the glycolytic pathway, lead to the conclusion that cyclic-AMP-dependent protein kinase is an extremely specific enzyme. The molecular basis of this specificity is discussed.

Debranching enzyme from rabbit skeletal muscle. Purification, properties and physiological role.

Abstract: Debranching enzyme was purified 150-fold from rabbit skeletal muscle by a three-step procedure which utilised ammonium sulphate precipitation, ion-exchange chromatography on DEAE-cellulose and “hydrophobic” chromatography on Sepharose-NH(CH2)4 NH2. The preparation was completed within three days, and 200 mg enzyme was isolated from 1000 g muscle, which represented an overall yield of 60 %. The preparation was homogeneous by the criteria of poly-acrylamide gel electrophoresis and ultracentrifugal analysis. The sedimentation coefficient, s20,w, was 8.1 S. The amino acid composition was determined, and the absorption coefficient, A1%280, measured refractometrically was 17.5. The subunit molecular weight determined by gel electrophoresis in the presence of sodium dodecyl sulphate was 166000 and this value was supported by sedimentation equilibrium in the presence of 6 M guanidinium chloride (155000). The molecular weight of the native enzyme measured by high-speed sedimentation equilibrium was 164000, showing that the debranching enzyme is a monomeric protein at the concentrations which exist in muscle (0.7 mg/ml). The results indicate that the two different enzyme activities which are associated with debranching enzyme, 1,4-glucan-4-glycosyltransferase and amylo-1,6-glucosidase, reside on the same polypeptide chain. Protein-glycogen particles isolated from skeletal muscle showed seven major protein-staining components by polyacrylamide gel electrophoresis, one of which was identified as debranching enzyme. Four of the other components were the α and β subunits of phosphorylase kinase, glycogen phosphorylase and glycogen synthetase. A new titrimetric assay for debranching enzyme was developed; it was used to demonstrate that the maximum potential activity of debranching enzyme is only 5–10% that of phosphorylase at the concentrations of the two enzymes in skeletal muscle. Since the activity of debranching enzyme is unaffected by every mechanism which leads to the activation of glycogen phosphorylase and phosphorylase kinase, the evidence suggests that the hormonal control of muscle glycogenolysis by adrenalin might be confined to a stimulation of rate of degradation of the outermost branches of glycogen.

The effect of calcium on gill potentials and on sodium and chloride fluxes in the goldfish,Carassius auratus

Abstract: Measurements of electric potential and of sodium and chloride effluxes were carried out on a freshwater fish, the goldfishCarassius auratus. The potential was affected by a number of inorganic ion species but that with the most significant influence on transepithelial potential was calcium. The potential was about 10 mV negative in the absence of calcium and about 10 mV positive in the presence of 10 mM/l calcium. Sodium and chloride efflux rates were greatly reduced upon the addition of calcium to the medium. The origin of the transepithelial potential is discussed in terms of the relative permeability of the branchial membranes to sodium and chloride and the factors influencing these permeabilities.

Proton translocation and the respiratory nitrate reductase of Escherichia coli.

Abstract: Stoicheometries and rates of proton translocation associated with respiratory reduction of NO3- have been measured for spheroplasts of Escherichia coli grown anaerobically in the presence of NO3-. Observed stoicheiometries [leads to H+/NO3- ratio; P. Mitchell (1966) Chemiosmotic Coupling in Oxidative and Photosynthetic Phosphorylation, Glynn Research, Bodmin] were approx. 4 for L-malate oxidation and approx. 2 for succinate, D-lactate and glycerol oxidation. Measurements of the leads to H+/2e- ratio with formate as the reductant and oxygen or NO3- as the oxidant were complicated by pH changes associated with formate uptake and CO2 formation. Nevertheless, it was possible to conclude that the site of formate oxidation is on the inner aspect of the cytoplasmic membrane, that the leads to H+/O ratio for formate oxidation is approx. 4, and that the leads to H+/NO3- ratio is greater than 2. Measurements of the rate of NO3- penetration into osmotically sensitive spheroplasts demonstrated an electrogenic entry of NO3- anion. The permeability coefficient for nitrate entry at 30 degrees C was between 10(-9) and 10(-10) cm- s(-1). The calculated rate of nitrate entry at the concentration typically used for the assay of nitrate reductase (EC 1.7.99.4) activity was about 0.1% of that required to support the observed rate of nitrate reduction by reduced Benzyl Viologen. Measurements of the distribution of nitrate between the intracellular and extracellular spaces of a haem-less mutant, de-repressed for nitrate reductase but unable to reduce nitrate by the respiratory chain, showed that, irrespective of the presence or the absence of added glucose, nitrate was not concentrated intracellularly. Osmotic-swelling experiments showed that the rate of diffusion of azid anion across the cytoplasmic membrane is relatively low in comparison with the fast diffusion of hydrazoic acid. The inhibitory effect of azide on nitrate reductase was not altered by treatments that modify pH gradients across the cytoplasmic membrane. It is concluded that the nitrate-reducing azide-sensitive site of nitrate reductase is located on the outer aspect of the cytoplasmic membrane. The consequences of this location for mechanisms of proton translocation driven by nitrate reduction are discussed, and lead to the proposal that the nitrate reductase of the cytoplasmic membrane is vectorial, reducing nitrate on the outer aspect of the membrane with 2H+ and 2e- that have crossed from the inner aspect of the membrane.

Ecological studies on algal‐lysing bacteria in fresh waters

Abstract: Summary Algal-iysing bacteria are present in five lochs, two reservoirs, one sewage works and five alkaline soils whieh were examined. Nine out of thirty-six isolates have been studied in detail and all are gram-negative non-fruiting myxobaeteria. All are aero-philic, require a neutral or alkaline pH (optimum 7.0–9.0) for good growth, have temperature optima of 28–37°C, require contact with the host for lysis to oecur, and are so similar in morphology and host range that they all appear to be strains of a single genus. They lyse all bloom-forming Cyanophyeeae on whieh they have been tested, including species of Anabaena, Aphanizomenon, Gloeotrichia, Microcystis and Oscillatoria. Their abundance is usually correlated direetly with the abundance of Cyanophyeeae in eutrophic waters and it is probable that in most ecosystems the algae and the bacteria co-exist, although if the equilibrium changes markedly as a result of change in environmental conditions situations may arise where the bacteria may play an important role in the lysis of algal blooms. The available evidence suggests, however, that this is likely to be a rare occurrence in natural ecosystems.

The solution of a mixed boundary value problem in the theory of diffraction by a semi-infinite plane

Abstract: A solution is obtained for the problem of the diffraction of a plane wave sound source by a semi-infinite half plane. One surface of the half plane has a soft (pressure release) boundary condition, and the other surface a rigid boundary condition. Two unusual features arise in this boundary value problem. The first is the edge field singularity. It is found to be more singular than that associated with either a completely rigid or a completely soft semi-infinite half plane. The second is that the normal Wiener-Hopf method (which is the standard technique to solve half plane problems) has to be modified to give the solution to the present mixed boundary value problem. The mathematical problem which is solved is an approximate model for a rigid noise barrier, one face of which is treated with an absorbing fining. It is shown that the optimum attenuation in the shadow region is obtained when the absorbing lining is on the side of the screen which makes the smallest angle to the source or the receiver from the edge.

Electron microscopical studies of the microflora of roots of sand dune grasses

Abstract: Summary Scanning and transmission electron microscopy were used to study microflora of roots of three species of sand dune grasses. Observations were made on the mucigel on intact epidermal cells and the colonization of sloughing superficial root cells by bacteria and actinomycetes. Thin sections of the same root samples showed that bacteria penetrated epidermal cells either by perforating the cell wall or by exploiting the middle lamella between adjacent cells as an avenue of entry. Cortical cells of all three species contained vesicular-arbuscular endophytes. Several phases of the mycorrhizal association could be identified.

Precambrian Crustal Development in Western Nigeria: Indications from the Iwo Region

Abstract: The rocks of the Iwo region of southwestern Nigeria comprise a migmatite-gneiss-granite complex and a metasupracrustal sequence. Though dominantly of amphibolite facies grade, pyroxene granulite and charnockite remnants are found in the migmatite-gneiss-granite complex. Old supracrustal remnants, best identified in resistant quartzite horizons, are also represented, and a variety of granitic plutonic rocks form well-marked circumscribed associations. The main metasupracrustal belt is associated with a major dislocation zone and has two principal lithologies — dominant amphibolite and pelite west of the fault zone and quartzite and quartzofeldspathic gneiss to the east. Oligoclase-granite gneiss and pegmatite are associated with the schist. All the rocks of the area have been affected to varying extents by late reworking, metasomatism, and granitic activity. On the basis of the indicated field relations and the limited radiometric age data available, a development sequence for the region is proposed. Archean crustal rocks are considered to have been involved in an Eburnian (1,950 ± 250 m.y.) reactivation of Proterozoic mobile belt type. In the Kibaran period (1,200 ± 200 m.y.), activity of greenstone belt–granite type brought about the formation of the Ife supracrustal–granite gneiss association, with extensive basement reactivation limited to the proximity of the downwarping supracrustal sequence. Late, widespread reworking and granitic plutonism is related to the Pan-African (Older Granite) event (600 ± 150 m.y.). The possible relevance of the proposed scheme to the interpretation of the development of the eastern parts of the West African platform is discussed.

Surface features of soybean root nodules

Abstract: The surface of turgid, nitrogen-fixing soybean root nodules is found to contain a number of prominent ridges on an otherwise smooth surface. Using the technique of critical point drying for tissue preparation, and scanning electron microscopy, these ridges were found to be lenticels, whose function is to permit the free movement of gases into and out of the nodule. The surface of the nodule between the lenticels contained no intercellular air spaces. The lenticels develop from a phellogen situated distal to a ring of sclereid cells in the nodule cortex. They develop as distinct “bands” of tissue immediately above and closely following the nodule vascular traces. When the nodules are subjected to conditions of water stress or waterlogging the most significant change to their surface is associated with the lenticels. In water stressed nodules the lenticel tissue collapses quickly, followed closely by shrinkage and collapse of the epidermis and outer cortex. In waterlogged nodules the lenticel tissues develop extensively with the production of large masses of loosely packed cells.

Studies on the initiation of bacterial soft rot in potato tubers

Abstract: Non-inoculated whole tubers rot readily under anaerobic conditions when their surface is maintained moist in a water-saturated atmosphere. Rotting is reduced under otherwise similar but aerobic conditions, but there is some rotting under anaerobic conditions even if their surface is dry.

Synthesis of alternative membrane-bound redox carriers during aerobic growth of Escherichia coli in the presence of potassium cyanide.

Abstract: Aerobic growth of Escherichia coli with an oxidizable substrate as carbon source in the presence of low concentrations of KCN leads to the synthesis and integration into the membrane of menaquinone and cytochromes b558, a1 and d in addition to the redox carriers normally present under aerobic growth conditions, namely ubiquinone and cytochromes b562, b556 and o. The results are discussed with reference to other phenotypic and genotypic modifications to the electron-transport chains of E. coli.

The Effect of pH on the Kinetics of Beef‐Liver Fructose Bisphosphatase

Abstract: 1. The kinetics of the reaction catalysed by fructose bisphosphatase have been studied at pH 7.2 and at pH 9.5. The activity of the enzyme was shown to respond sigmoidally to increasing concentrations of free Mg2+ or Mn2+ ions at pH 7.2, whereas the dependence was hyperbolic at pH 9.5. At both pH values the enzyme responded hyperbolically to increasing concentrations of fructose 1,6-bisphosphate, although inhibition was observed at higher concentrations of this substrate. This high substrate inhibition was shown to be partial in nature and the enzyme was found to be more sensitive at pH 7.2 than at pH 9.5. 2. The properties of the enzyme, are consistent with the enzyme obeying either a random-order equilibrium mechanism or a compulsory-order steady-state mechanism in which fructose bisphosphate binds to the enzyme before the cation. 3. Reaction of the enzyme with a four-fold molar excess of p-chloromercuribenzoate caused activation of the enzyme when its activity was assayed in the presence of MN2+ ions but inhibition when Mg2+ ions were used. Higher concentrations of p-chloromercuribenzoate caused inhibition. This activation at low p-chloromercuribenzoate concentrations, and the reaction of 5,5'-dithio-bis(2-nitrobenzoate) with the four thiol groups in the enzyme that reacted rapidly with this reagent, were prevented or slowed by the presence of inhibitory, but not non-inhibitory, concentrations of fructose bisphosphate. After reaction with a four-fold molar excess of p-chloromercuribenzoate the enzyme was no longer sensitive to high substrate inhibition by fructose bisphosphate.

Monocular and Binocular Rivalry between Contours

Abstract: The temporal characteristics of binocular and monocular rivalry between orthogonal gratings of the same or complementary colours were investigated. Rivalry was measured in terms of the dominance of either grating or the visibility of composites comprised of parts of both gratings. The total duration for which either grating was dominant was significantly longer in binocular rivalry between gratings of complementary colours. A comparison of binocular and monocular rivalry indicated considerable phenomenal differences between them. Dominance in binocular rivalry corresponds to the visibility of one grating alone; this occurs rarely in monocular rivalry, which is characterized by fluctuations in the distinctiveness of the gratings. The changes in distinctiveness are influenced by colour in a similar manner to that in binocular rivalry, and the frequencies of fluctuations are higher for gratings of complementary colours.

Effects of sulphate-limited growth in continuous culture on the electron-transport chain and energy conservation in Escherichia coli K12.

Abstract: Growth of Escherichia coli K12 in a chemostat was limited by sulphate concentrations lower than 300 muM. The synthesis of extracellular polysaccharide and a change in morphology accompanied sulphate-limited growth. Growth yields with respect to the amount of glycerol or oxygen consumed were sixfold and twofold lower respectively under these conditions than when growth was limited by glycerol. Sulphate-limited cells lacked the proton-translocating oxidoreduction segment of the electron-transport chain between NADH and the cytochromes, and particles prepared from these cells lacked the energy-dependent reduction of NAD+ by succinate, DL-alpha-glycerophosphate or D-lactate, suggesting the loss of site-I phosphorylation. Glycerol-limited cells contained cytochrome b556, b562 and o, ubiquinone and low concentrations of menaquinone. Sulphate limitation resulted in the additional synthesis of cytochromes d, a1, b558 and c550; the amount of ubiquinone was decreased and menaquinone was barely detectable. Non-haem iron and acid-labile sulphide concentrations were twofold lower in electron-transport particles prepared from sulphate-limited cells. Recovery of site-I phosphorylation could not be demonstrated after incubating sulphate-limited cells with or without glycerol, in either the absence or presence of added sulphate. The loss of site-I phosphorylation in sulphate-limited cells is discussed with reference to the accompanying alterations in cytochrome composition of such cells. Schemes are proposed for the functional organization of the respiratory chains of E. coli grown under conditions of glycerol or sulphate limitation.

The reactions of glutaraldehyde with nucleic acids.

Abstract: The kinetics of the reactions between glutaraldehyde, RNA and DNA have been investigated. At temperatures up to 64 degree C no reaction occurred between native DNA and glutaraldehyde. At temperatures above 75 degree C the reaction followed pseudofirst order kinetics, proceeding more quickly at higher temperatures. Reactions between RNA and glutaraldehyde were similar, except that they began above 45 degree C. These findings were corroborated by thermal transition profiles. There was little evidence for the formation of cross-links between nucleic acid molecules even at elevated temperatures.

Tungsten coating—a method of improving glass microtome knives for cutting ultrathin sections

Abstract: SUMMARY Glass knives for ultramicrotomy were considerably improved by coating the cutting edge with a film of evaporated tungsten metal. Knives treated by this method gave up to ten times as many acceptable sections as uncoated glass knives. They could also cut thinner sections and harder tissues than ordinary glass knives, and eliminated some of the cutting artefacts produced by them. No explanation for this improvement was found although several possibilities were examined.

The allosteric properties of beef-liver fructose bisphosphatase.

Abstract: 1. The activity of beef liver fructose bisphosphatase has been shown to respond cooperatively to increasing concentrations of the activating cations Mg2+ and Mn2+. The allosteric inhibitor AMP caused an increase in this cooperativity and a decrease in the apparent affinity of the enzyme for the activating cation. 2. The cooperative response of the enzyme to AMP is similarly increased by increasing cation concentrations with a concomitant decrease in the apparent affinity. 3. Direct binding experiments indicated that in the absence of either Mg2+ or Mn2+ the enzyme bound AMP non-cooperatively up to a maximum of two molecules per molecule of enzyme, a result that is indicative of half-sites reactivity. The binding became increasingly cooperative as the concentration of the activating cation was increased. 4. The substrate fructose bisphosphate had no effect on any of these cooperative responses. 5. These results may be most simply interpreted in terms of concerted model in which the activating cation functions both as an allosteric activator and as an essential cofactor for the reaction.

Polyhedral bodies (carboxysomes) of nitrogen-fixing blue-green algae

Abstract: Blue-green algae possess polyhedral bodies which, under the electron microscope, resemble the carboxysomes containing ribulose-1-5-diphosphate carboxylase (RUDPCase) in the chemoautotrophic bacterium Thiobacillus. These bodies are present in vegetative cells but not the heterocysts of 15 strains of Anabaena, Nostoc, Plectonema and Westiellopsis, including material grown photoautotrophically, photoheterotrophically and dark heterotrophically. They are also present in spores (akinetes). Their absence from heterocysts provides morphological evidence in support of the view that heterocysts are deficient in RUDPCase.