Showing papers by "University of Dundee published in 1982"
TL;DR: There is an integrated network of regulatory pathways, mediated by phosphorylation–dephosphorylation, that allows diverse cellular events to be coordinated by neural and hormonal stimuli, and the evidence that supports this concept is reviewed.
Abstract: Protein phosphorylation is now recognized to be the major general mechanism by which intracellular events in mammalian tissues are controlled by external physiological stimuli However, only recently has the idea that different cellular functions are controlled by common protein kinases and protein phosphatases started to gain widespread acceptance Thus there is an integrated network of regulatory pathways, mediated by phosphorylation-dephosphorylation, that allows diverse cellular events to be coordinated by neural and hormonal stimuli The evidence that supports this concept is reviewed, with emphasis on the role of protein phosphorylation in enzyme regulation
1,065 citations
TL;DR: The comparison of these brain-wave sequences to those elicited by the same stimuli in reading subjects led to the conclusion that in detection conditions, deviant stimuli elicit two overlapping sequences of brain events: exogeneous and endogeneous.
586 citations
454 citations
TL;DR: The serine residue on the a-sub unit, as well as that on the@subunit, becomes phosphorylated in vivo in response to adrenaline, suggesting that it may have a physiological function.
453 citations
TL;DR: The nucleotide sequence of the entire histidine transport operon from Salmonella typhimurium has been determined and is shown to consist of four genes, hisJ, hisQ, hisM and hisP.
Abstract: The nucleotide sequence of the entire histidine transport operon from Salmonella typhimurium has been determined and is shown to consist of four genes, hisJ, hisQ, hisM and hisP. This operon provides the only example of a binding protein-dependent transport system for which the total number of protein components is known. Determination of the amino acid compositions and sequences of these four transport proteins, together with analysis of various transport mutants, allows us to propose a molecular model for binding protein-dependent transport.
306 citations
TL;DR: A genetic element is identified, common to intercistronic regions from three independent bacterial operons, which is believed to be important in regulating the differential expression of individual genes in these multicistronic operons.
Abstract: The nucleotide sequences of the intercistronic regions from several multicistronic operons have recently been determined. In many cases such intercistronic regions consist of only a few base pairs (bp); in certain extreme cases, where the initiation codon of one gene overlaps the termination codon of the previous gene, intercistronic regions are essentially absent1,2. However, in other cases intercistronic regions can be up to several hundred base pairs long; it seems reasonable to suppose that, at least in these cases, such regions have a role in regulating expression of the operon. Indeed, a regulatory function for the large intercistronic region of the rplJL–rpoBC operon has been demonstrated3. We have now identified a genetic element, common to intercistronic regions from three independent bacterial operons (the histidine transport and the histidine biosynthetic operons of Salmonella typhimurium and the malK–lamB operon of the malB region of Escherichia coli), which we believe to be important in regulating the differential expression of individual genes in these multicistronic operons. A similar element is also found immediately following the trpR gene of E. coli although in this case it is not known whether or not a distal gene exists. Each of these elements consists of a long dyad symmetry which, once transcribed, could form an exceptionally stable stem–loop structure with a stem of up to 35 bp. In each case smaller palindromic units are also found, some of which overlap the main symmetry. The stem–loop structures show remarkable homology (---90%) and probably have a common evolutionary origin, possibly an insertion element. It seems that the function of these structures is to effect a decrease in expression of distal genes in an operon.
289 citations
TL;DR: The NH2‐terminal blocking group of the Ca 2+‐binding B‐subunit of calcineurin (protein phosphatase‐2B) has been identified as myristic acid by fast atom bombardment mass spectrometry and gas chromatography and may facilitate the identification of other proteins with this blocking group.
277 citations
TL;DR: In this article, a model involving impeded drainage is proposed, which is in better accord with the structure of the peat and with basic tenets of soil physics, and the elliptical shape and proportions of the mire surface profile are in agreement with this model.
Abstract: Raised mires are ecosystems in which waterlogged peat accumulates above the level of the surrounding stream system. It has been suggested that waterlogging is maintained by matric forces, but a model involving impeded drainage is in better accord with the structure of the peat and with basic tenets of soil physics. At one site from which enough hydrological and soil physical data are available to conduct a preliminary test, the elliptical shape and proportions of the mire surface profile are in agreement with this model.
267 citations
TL;DR: It is suggested that patients come to be defined as good or bad not because of anything inherent in them or in their behaviour, but as a consequence of the interaction between staff and patients.
Abstract: Nursing, sociological and psychological research into good and bad, popular and unpopular, and desirable and undesirable patients is reviewed. A number of themes which have been linked by researchers with the evaluation of good and bad patients are identified. These are patients' illnesses and diseases, patients' behaviour, the social backgrounds of patients, patients' attitudes and staff attitudes. It is argued that much of the literature on good and bad patients is deficient from an empirical, a methodological, an epistemological and a theoretical point of view. An alternative theoretical framework is suggested, using as its starting point an interactionist conception of the nursing role. It is suggested that patients come to be defined as good or bad not because of anything inherent in them or in their behaviour, but as a consequence of the interaction between staff and patients.
221 citations
TL;DR: In this article, it was shown that large units are no less efficient and can be a good deal more effective than small ones, and that in some respects they may be more so.
Abstract: Arguments about the optimum size for units of local government often overlook the fact that small units have some considerable drawbacks while large ones have some advantages. By and large the discussion breaks down into two parts; those about size and functional effectiveness, and those about size and democracy. On the first count, it seems that large units are no less efficient and can be a good deal more effective than small ones. On the question of size and democracy, the evidence suggests that large units of government are no less democratic than small ones, and that in some respects they may be more so.
185 citations
TL;DR: The results prove that proteinosphatase‐1 and the Mg‐ATP‐dependent protein phosphatase contain the same catalytic subunit, and that they are interconvertible forms of the same enzyme.
TL;DR: Although phosphorylation of site 5 does not affect the catalytic activity, it is demonstrated that this modification is a prerequisite for phosphorylated by glycogen synthase kinase‐3.
TL;DR: Three glycogen synthase kinases, which are distinct from cyclic-AMP-dependent protein kinase and phosphorylase kinase, have been purified and characterised and did not phosphorylate any other proteins tested at a significant rate.
Abstract: Three glycogen synthase kinases termed glycogen synthase kinase 3, glycogen synthase kinase 4 and glycogen synthase kinase 5, which are distinct from cyclic-AMP-dependent protein kinase and phosphorylase kinase,have been purified and characterised. Their activities are unaffected by Ca2+, calmodulin, cyclic nucleotides and the inhibitor protein of cyclic-AMP-dependent protein kinase.
Glycogen synthase kinase 3 was eluted from phosphocellulose at 0.2 M NaCl and the apparent M, of the partially purified enzyme determined by gel filtration in the presence of 0.5 M NaCl was 72000. Glycogen synthase kinase 3 used GTP as a substrate (VGTp/VATp= 0.65) but the apparent affinity for GTP (Km= 0.4 mM) was lower than that for ATP (Km= 0.02 mM). Glycogen synthase kinase 3 phosphorylated three serine residues (sites 3a, 3b and 3c) on glycogen synthase, but seven other proteins that are phosphorylated rapidly by cyclic-AMP-dependent protein kinase were not substrates for glycogen synthase kinase 3. Glycogen synthase kinase 3 phosphorylated casein at a very low rate and did not phosphorylate phosvitin, although a protein of M1= 35000 which contaminated phosvitin to avariable extent was a good substrate. Glycogen synthase kinase 3 was the only enzyme capable of activating the (Mg-ATP)-dependent protein phosphatase.
Glycogen synthase kinase 4 was eluted from phosphocellulose at 0.4 M NaCl and its apparent M, was 115000.This enzyme was absolutely specific for ATP as phosphoryl donor (Km=0.01 mM), and it phosphorylated glycogen synthase at the same serine residue as phosphorylase kinase (site 2). Glycogen synthase kinase 4 was distinct from phosphorylase kinase since its activity was unaffected by Ca2+ or calmodulin, it had a quite different M, and nucleoside triphosphate specificity, and it could not phosphorylate glycogen phosphorylase.Glycogen synthase kinase 4 did not phosphorylate any other proteins tested at a significant rate.
Glycogen synthase kinase 5 was eluted from phosphocellulose at 0.7 M NaCl and its apparent M, was 170000–180000. This enzyme could use GTP as a substrate (YGTP VATP= 0.85) and the apparent affinities for GTP(K, = 0.04 mM) and ATP (Km = 0.01 mM) were similar. Glycogen synthase kinase 5 phosphorylated a single serine residue on glycogen synthase, termed site 5 and the sequence surrounding this site was found to be His-Ser-Ser-Pro-His-Gln-Ser (PGlu-Asp-Glu-Glu-Glu-Pro.
The phosphorylation of site 5 did not decrease the activity of glycogen synthase in contrast to the phosphorylation by other glycogen synthase kinases. Glycogen synthase kinase 5 phosphorylated casein, phosvitin and acetyl-CoA carboxylase more rapidly than glycogen synthase, but did not phosphorylate other proteins tested. Glycogen synthase kinase 5 was activated sixfold by spermine at 5.7 mM Mg2+ and 40–50-fold at 1.2 mM Mg2+, and was powerfully inhibited by heparin (Ki= 0.04 pg/ml).
40–50% of the glycogen synthase kinase 5 was precipitated when muscle extracts were acidified to pH 6.1, whereas glycogen synthase kinase 3 remained in the supernatant. When the supernatant was chromatographed on phosphocellulose, glycogen synthase kinase 3 accounted for 84–92%, glycogen synthase kinase 4 for 5 – 7 and glycogen synthase kinase 5 for 0.2 -10% of the glycogen synthase kinase activity that was eluted from the column, depending on the concentration of NaCl, Mg2+ and spermine used in the assays.
Purified phosphorylase kinase contained detectable amounts of glycogen synthase kinase 5, and contamination by this enzyme accounts for reports that phosphorylase kinase can phosphorylate glycogen synthase at a site distinct from site 2.
Most, if not all, of the glycogen synthase kinases reported in the literature (other than cyclic-AMP-dependent protein kinase and phosphorylase kinase), can now be identified as glycogen synthase kinases 3, 4 or 5, or combinations of two of these enzymes. The properties of glycogen synthase kinase 5 demonstrate that it is identical to the enzyme that has been termed casein kinase TS, casein kinase 2 or troponin-T kinase.
TL;DR: Amorphous carbon films have been prepared from gas mixtures containing small predetermined amounts of phosphine, diborane or nitrogen as discussed by the authors, and it is concluded that conduction is predominantly by hopping in a region of fairly...
Abstract: Amorphous carbon films have been prepared in a r.f. glow discharge from various hydrocarbon gases. Electrical conductivity and optical absorption measurements show a strong dependence on the preparation gas and on the substrate temperature T d. Particularly for specimens prepared from ethylene, varying T d from 230 to 300°C increased the conductivity by ten orders of magnitude and decreased the optical gap from 2·0 to 0·8 eV. The hydrogen content of the specimens, measured by the thermal evolution technique, lies between 30% and 45% and shows no systematic dependence on T d or the preparation gas. Results are also presented for films which have been prepared from gas mixtures containing small predetermined amounts of phosphine, diborane or nitrogen. The addition of each dopant gas increases the specimen conductivity by between one and three orders of magnitude, depending on T d. It is concluded that for both undoped and doped specimens, conduction is predominantly by hopping in a region of fairly...
TL;DR: In this paper, the authors investigated the SCLC flow as a function of applied potential, temperature and specimen thickness in amorphous silicon films prepared by the glow-discharge technology.
Abstract: Space-charge-limited current (SCLC) flow has been investigated as a function of applied potential, temperature and specimen thickness in amorphous silicon films prepared by the glow-discharge techn...
TL;DR: It is concluded that fatty acids are the most plausible acute regulators of the proton conductance of the hamster brown-fat mitochondrial proton-conductance pathway.
Abstract: Possible mechanisms are evaluated for the acute regulation of the hamster brown-fat mitochondrial proton-conductance pathway which is active during non-shivering thermogenesis. Isolated mitochondria are incubated under conditions designed to approximate to the non-thermogenic state, and the effect of the steady infusion of fatty acids or acyl derivatives upon respiration, membrane potential and membrane proton conductance is monitored continuously. Fatty acids increase the proton conductance with no detectable threshold concentration, allowing the generated acyl carnitine to be rapidly oxidized. The extent of depolarization and of respiratory increase is a function of the rate of infusion. Immediately infusion is terminated the conductance decreases, the mitochondria repolarize and respiration returns to the initial rate. Infusion of acyl-CoA and acylcarnitine cause only a slight depolarization or respiratory increase after high concentrations of these derivatives have accumulated. Any factor which decreases the rate of conversion of fatty acid to acyl-CoA potentiates the conductance increase. An effect of acyl-CoA upon chloride permeability is not specific to brown-fat mitochondria. Fatty acids infused into rat liver mitochondrial incubations produced a small conductance increase, comparable to that of acyl-CoA or acylcarnitine. It is concluded that fatty acids are the most plausible acute regulators of the proton conductance. The relation to the brown-fat-specific 32000-Mr protein is discussed.
01 Jan 1982
TL;DR: If the technique of a step restriction (or trust region) is incorporated into the algorithm, then it is shown that global convergence can be proved.
Abstract: Composite functions ϕ(x)=f(x)+h(c(x)), where f and c are smooth and h is convex, encompass many nondifferentiable optimization problems of interest including exact penalty functions in nonlinear programming, nonlinear min-max problems, best nonlinear L 1, L 2 and L ∞ approximation and finding feasible points of nonlinear inequalities. The idea is used of making a linear approximation to c(x) whilst including second order terms in a quadratic approximation to f(x). This is used to determine a composite function ψ which approximates ϕ(x) and a basic algorithm is proposed in which ψ is minimized on each iteration. If the technique of a step restriction (or trust region) is incorporated into the algorithm, then it is shown that global convergence can be proved. It is also described briefly how the above approximations ensure that a second order rate of convergence is achieved by the basic algorithm.
TL;DR: The lack of an effect of total matrix Ca content on the efflux rate in the presence of Pi is used as the basis of a highly accurate determination of the activity of the Ca uniporter as a function of external free Ca concentration.
Abstract: The rate of spontaneous efflux of Ca from liver mitochondria incubated in the absence of ATP and Mg increases with time and is associated with a synchronous collapse of membrane potential and with Pi efflux. In the presence of Mg and ATP the ruthenium-red-induced Ca efflux does not change with time. The activity of the Ca efflux pathway in Pi-depleted mitochondria is 15-fold greater than in mitochondria equilibrated with 3.3 mM Pi. 50% inhibition is caused by 0.3 mM Pi. The membrane potential is not affected by changes in Pi concentration, although the steady-state extra-mitochondrial free Ca concentration reflects the alterations in efflux rate. In the presence of Pi, the ruthenium-red-induced efflux rate is independent of the total matrix Ca content; however in Pi-depleted mitochondria, with acetate substituting as permeant anion, the efflux rate increases with total matrix Ca content. The lowered efflux rate in the presence of Pi is not due to a limitation in the rate of dissociation of the matrix Ca-phosphate complex. The efflux pathway is activated by a lowered membrane potential, but the relative effect of Pi is retained. Under the present conditions Na slightly inhibits the efflux rate. The lack of an effect of total matrix Ca content on the efflux rate in the presence of Pi is used as the basis of a highly accurate determination of the activity of the Ca uniporter as a function of external free Ca concentration.
TL;DR: The growth habit of Cladophora and, particularly, Ranunculus means that the high water velocity in the Burn does not necessarily prevent C depletion effects around the plants, thus providing a possible role for HCO3-use by these plants.
Abstract: CO2-and O2-exchange characteristics and δ13C values have been measured in a rhodophycean haptophyte (Lemanea mamillosa), a chlorophycean haptophyte (Cladophora glomerata) and a magnoliophyte rhizophyte (Ranunculus sp.) from a 5 m stretch of the Dichty Burn near Dundee. Light-and CO2-saturated rates of photosynthesis are greatest on a dry weight basis for Cladophora and lowest for Lemanea; the order is reversed on a surface area basis. The CO2 concentration at pH 6.5 at which photosynthesis is half-saturated is 25-40 μM, with Lemanea rather lower than Cladophora or Ranunculus; these half-saturation values are similar to the free CO2 concentration in the Burn water. Lemanea cannot use HCO 3- in photosynthesis, while Cladophora and Ranunculus can. Despite being within a factor or two of saturation with free CO2 in terms of the bulk water concentration, the growth habit of Cladophora and, particularly, Ranunculus means that the high water velocity in the Burn does not necessarily prevent C depletion effects around the plants, thus providing a possible role for HCO 3- use by these plants. Lemanea lives in the fastest-growing parts of the Burn, and its growth habit insures that it is exposed to this high water velocity, thus minimising CO2 depletion during photosynthesis despite the low surface/volume ratio for this plant. δ13C measurements on the inorganic C in the Burn water are consistent with at least part of its excess (above air-equilibrium) inorganic C levels coming from heterotrophic activity. Lemanea has the most negative δ13C value of the three plants, consistent with CO2 use and small diffusion resistances. Ranunculus has the least negative δ13C value, consistent with some CO2 depletion and/or HCO 3- use in situ related to a high diffusion resistance in a rhizophyte which does not have to obtain all of its N and P from the bulk water but can obtain some from the sediments. Cladophora is intermediate, suggesting some CO2 depletion and/or HCO 3- use in this densely growing haptophyte.
01 Apr 1982
TL;DR: In this article, the authors report preliminary data on the characteristics of a new electronic switching device based on amorphous silicon structures; the device is polar, and is switched from OFF to ON (WRITE) or ON to OFF (ERASE) by voltages opposite signs.
Abstract: The paper reports preliminary data on the characteristics of a new electronic switching device based on amorphous silicon structures. The device is polar, and is switched from OFF to ON (WRITE) or ON to OFF (ERASE) by voltages opposite signs; the threshold voltage for the WRITE operation is 4 ?8 V, depending on the device, and for ERASE it is ? 1 V. The OFF and ON resistances are typically l M?, and in the range 50?300?, respectively. Experimental devices have been switched through 105 WRITE and ERASE cycles, and the prospects are that this could be considerably increased. Particularly notable features of the new memory device are its extremely fast transition times (100 ns or less for both the WRITE or ERASE operations) and the very low energy involved in the switching transition (<10?6 J). Present results indicate that the threshold voltages are only slightly dependent on temperature.
TL;DR: In the parotid gland, ATP evokes a marked increase in membrane conductance, radioactive Rb efflux and amylase secretion, similar to those evoked by acetylcholine and α-adrenergic agonists but are still present when cholinergic and adrenergic blocking agents are used.
Abstract: ATP and other purine nucleotides and nucleosides have potent regulatory (neurotransmitter-like) actions which have been attributed to interaction with a specific plasma membrane receptor1. To date the receptor mechanisms underlying purinergic activation have been poorly characterized. One problem has been the variability of the evoked effects in different tissues. Burnstock2,3 proposed that much of the variability could be explained if the effects were mediated by two separate receptors, termed P1 and P2, with different specificities for agonists and antagonists. Receptor mechanisms have been extensively investigated in the parotid gland4. I now report that in that gland, ATP evokes a marked increase in membrane conductance, radioactive Rb efflux and amylase secretion. The effects of ATP are similar to those evoked by acetylcholine (ACh) and α-adrenergic agonists but are still present when cholinergic and adrenergic blocking agents are used. The latency and reversal potential of the ATP-evoked effects are comparable with those of the autonomic agonists. The ATP receptor on parotid acinar cells is of the P2 type2,3, since the order of potency of the nucleotide series was ATP>ADP≫AMP, adenosine had no effect, and the response could be blocked by quinidine but not by theophylline.
TL;DR: The relevance of continued exposure to common allergens and their involvement in photosensitization mechanisms is discussed in an attempt to explain the state of ‘persistent light reaction.’
Abstract: Contact allergic sensitivity to allergens such as plants of the Compositae family is a feature of the chronic skin reaction seen in the photosensitivity dermatitis with actinic reticuloid syndrome. In fifty patients with this syndrome an increased incidence of contact allergic sensitivity to some common fragrance materials was demonstrated. Evidence is also presented, both by in vitro and in vivo studies, which indicates that a phototoxic mechanism is involved. The relevance of continued exposure to common allergens and their involvement in photosensitization mechanisms is discussed in an attempt to explain the state of 'persistent light reaction'.
TL;DR: The effect of alpha-latrotoxin from black widow spider venom upon guinea pig cerebral cortical synaptosomes is described and release of [3H]noradrenaline and gamma-amino[ 3H]butyrate is markedly stimulated by the toxin in the presence of Ca2+, and this effect is only slightly reduced in Ca2+-free conditions.
Abstract: The effect of alpha-latrotoxin from black widow spider venom upon guinea pig cerebral cortical synaptosomes is described. Plasma membrane potential (delta psi p), in situ mitochondrial membrane potential (delta psi m), Ca2+ transport, gamma-amino[3H]butyrate release, [3H]noradrenaline release, and synaptosomal ATP were monitored under parallel conditions. Potentials were determined both isotopically and with a tetraphenylphosphonium-selective electrode. alpha-Latrotoxin depolarizes delta psi p selectively, both in the presence and absence of Ca2+. A slight toxin-induced depolarization of delta psi m is a consequence of a massive Ca2+ uptake across the plasma membrane. Depolarization of delta psi p is insensitive to tetrodotoxin, and Ca2+ entry is only partially inhibited by verapamil. Release of [3H]noradrenaline and gamma-amino[3H]butyrate is markedly stimulated by the toxin in the presence of Ca2+, and this effect is only slightly reduced in Ca2+-free conditions.
TL;DR: It is suggested that the C02 accumulating mechanism results in essentially a closed system in which the inherent isotope discrimination by RuBP carboxylase is not expressed.
Abstract: The relationship between the C02 accumulating mechanism and carbon isotope discrimination has been investigated in the unicellular green alga Chlorella emersonii. Growth of Chlorella at high C02 levels (5%) which repress the activity of the C02 accumulating mechanism results in more negative AonC values. The data presented in this paper suggest that it is possible to induce the accumulating mechanism by nitrogen limitation as well as by carbon limitation. Activity of the accumulating mechanism, irrespective of whether it is induced by C or by N limitation, is accompanied by ?1<513C values considerably less negative than those of cells which do not possess such a mechanism. It is suggested that the C02 accumulating mechanism results in essentially a closed system in which the inherent isotope discrimination by RuBP carboxylase is not expressed.
TL;DR: In this paper, a series of laboratory investigations have been performed on the flow past a right circular cylinder in a rotating water channel, where the upper and lower surfaces of the channel have been tilting so that the depth of the fluid varies in the cross-stream direction.
Abstract: With a view to obtaining a fuller understanding of the interactions between topography and large-scale geophysical flows, a series of laboratory investigations have been performed on the flow past a right circular cylinder in a rotating water channel. For large-scale flows on a spherical Earth the variation of the Coriolis parameter, F = 2Ωsinϕ , with latitude, ϕ, is commonly written (Pedlosky 1979) as F = f + β 0 y where f = 2Ωsinϕ o , β o = 2Ωcosϕ o /R E , y is the distance to the north from the reference latitude ϕ o , and R E and Ω( = 7.29 x 10 -5 s-1 ) are the radius and rotation rate of the Earth respectively. In this paper we shall discuss laboratory experiments in which the variation of F can be simulated. We shall refer to those studies in which β = 0 (i.e. the Coriolis parameter is uniform over the latitudinal extent of the region under investigation) as f-plane experiments. Models for which β o is non-zero will be referred to as β-plane experiments. In the experiments the β-effect has been simulated by tilting the upper and lower surfaces of the channel so that the depth of the fluid varies in the cross-stream direction. Flow patterns have been obtained over a range of five independent non-dimensional parameters: Rossby and Ekman numbers, cylinder aspect ratio, β-parameter and flow direction (‘eastward’ or ‘westward’). A dramatic difference in downstream behaviour is found between f-plane, β-plane westward and /plane eastward flows. In particular, the β-plane eastward flows are characterized by bunching and pinching of streamlines in the wake region, the generation of damped stationary Rossby waves and downstream acceleration. Compared with f-plane flows the β-effect is shown to inhibit boundary layer separation from the cylinder for eastward flow and to enhance the separation for westward flow. Data are presented from all cases to show the asymmetry of the downstream flows and the transitions from fully attached to unsteady flows. Under otherwise identical conditions the downstream extent of the separated bubble region is much greater for β-plane westward flow than, in turn, for f-plane and β-plane eastward flows. In addition, the data indicate that the size of the bubble increases with increasing Rossby number and decreases with increasing Ekman number and cylinder aspect ratio. For eastward flow the bubble size decreases with increasing β-parameter and for westward flow it increases with increasing β-parameter. Unsteady flows are investigated and instances of asymmetrical vortex shedding are presented.
TL;DR: It appears that the majority of freshwater algae have genetic capabilities to produce both walls and contractile vacuoles for cell volume regulation, and these conclusions may be used in the interpretation of such phenomena as the lower osmolarity of wall-less than walled cells and the tendency for the resting stages of normally wall- less and flagellate cells to have walls.
Abstract: SUMMARY
Freshwater algae have an intracellular osmolarity in excess of that of the medium. The tendency for water to enter the cells is resisted, in cells with a mechanically functional cell wall, by the ability of the wall to withstand a turgor pressure equivalent to the intracellular osmolarity; in cells lacking such a mechanically functional wall the water which enters is expelled by a contractile vacuole (or its functional equivalent). A comparison of the energy costs of cell volume regulation by these two mechanisms has been carried out making energy costings based on the minimum thermodynamic requirement and on plausible mechanisms for the two processes (wall synthesis and contractile vacuole function). This analysis yielded the following conclusions.
(1) Wall synthesis is a ‘growth’ process, while contractile vacuole operation is a’maintenance’process; other things being equal, a cell wall is a preferable mechanism of volume regulation in non-growing cells.
(2) For a 5 μm radius cell with a specific growth rate of 8 × 10−6 s−1 and a 10 μm radius cell with a rate of 4 × 10−6 s−1 the energy input rate for contractile vacuole operation is considerably lower than for wall synthesis on the basis of minimum thermodynamic requirement; the plausible mechanism approach makes the two energy costs quite similar. Decreased growth rates favours the wall over the contractile vacuole mechanism.
(3) Increased cell size (10 μm radius rather than 5 μm) has similar effects on the energy costs of both volume regulation mechanisms, provided a (cell organic weight)−0.32 dependence of intrinsic growth rate is incorporated into the computations.
(4) Increased intracellular osmolarity (at constant extracellular osmolarity) causes a directly proportional increase in energy input rate for the cell wall mechanism, and a more than proportional increase in energy cost for the contractile vacuole mechanism.
(5) A non-spherical shape increases the energy cost (at constant cell volume) for both the cell wall and the contractile vacuole mechanisms.
These conclusions may be used in the interpretation of such phenomena as the lower osmolarity of wall-less than walled cells and the tendency for the resting stages of normally wall-less and flagellate cells to have walls. It appears that the majority of freshwater algae have genetic capabilities to produce both walls and contractile vacuoles for cell volume regulation (e.g, the production of walled cysts by organisms which are normally flagellate, and the production of wall-less motile spores and gametes by normally walled organisms).
TL;DR: It is concluded that the presence of the 32000-Mr proton conductance pathway is necessary for the expression of a high sensitivity to fatty acid uncoupling, suggesting that the fatty acids interact directly with this protein to modulate the proton Conductance during the acute regulation of thermogenesis.
Abstract: Cells and mitochondria were prepared from the brown adipose tissue of adult guinea-pigs adapted to either 4–7°C or 22–25°C. The cold-adapted cells displayed noradrenaline-stimulated, propranolol-sensitive respiration, but noradrenaline failed to increase the respiration of the warm-adapted cells. Purine-nucleotide-sensitive proton conductance was greater in cold-adapted mitochondria than in warm-adapted controls. At the same time cold-adapted mitochondria were extremely sensitive to the uncoupling effect of endogenous and infused fatty acids, and resembled the mitochondria from the brown adipose tissue of cold-adapted hamsters. Warm-adapted mitochondria were ninefold less sensitive, and resembled liver mitochondria. With cold-adapted, but not warm-adapted mitochondria, respiration increased proportionately to the rate of fatty acid infusion. It is concluded that the presence of the 32000-Mr proton conductance pathway is necessary for the expression of a high sensitivity to fatty acid uncoupling, suggesting that the fatty acids interact directly with this protein to modulate the proton conductance during the acute regulation of thermogenesis.