Note on oscillations of turbidity in a precipitation reaction system of thyroxine

A model for a precipitation reaction system is presented in which all steps are reversible monomolecular or bimolecular reactions. Under certain conditions, quasi-stable oscillations in turbidity can occur, as has been observed in the precipitation of thyroxine.     

Isoforms of the invariant chain regulate transport of MHC class II molecules to antigen processing compartments

Newly synthesized class II molecules of the major histocompatibility complex must be transported to endosomal compartments where antigens are processed for presentation to class II-restricted T cells. The invariant chain (Ii), which assembles with newly synthesized class II alpha- and beta-chains in the endoplasmic reticulum, carries one or more targeting signals for transport to endosomal compartments where Ii dissociates from alpha beta Ii complexes. Here we show that the transport route of alpha beta Ii complexes is regulated selectively by two forms of Ii (p33 and p35) that are generated by the use of alternative translation initiation sites. Using a novel quantitative surface arrival assay based on labeling with [6-3H]-D-galactose combined with biochemical modification at the cell surface with neuraminidase, we demonstrate that newly synthesized alpha beta Ii molecules containing the Ii-p33 isoform can be detected on the cell surface shortly after passage through the Golgi apparatus/trans-Golgi network. A substantial amount of these alpha beta Ii complexes are targeted to early endosomes either directly from the trans-Golgi network or after internalization from the cell surface before their delivery to antigen processing compartments. The fraction of alpha beta Ii complexes containing the p35 isoform of Ii with a longer cytosolic domain was not detected at the cell surface as determined by iodination of intact cells and the lack of susceptibility to neuraminidase trimming on ice. However, treatment with neuraminidase at 37 degrees C did reveal that some of the alpha beta Ii-p35 complexes traversed early endosomes. These results demonstrate that a fraction of newly synthesized class II molecules arrive at the cell surface as alpha beta Ii complexes before delivery to antigen processing compartments and that class II alpha beta Ii complexes associated with the two isoforms of Ii are sorted to these compartments by different transport routes.     

Generation of nonidentical compartments in vesicular transport systems

How can organelles communicate by bidirectional vesicle transport and yet maintain different protein compositions? We show by mathematical modeling that a minimal system, in which the basic variables are cytosolic coats for vesicle budding and membrane-bound soluble N-ethyl-maleimide–sensitive factor attachment protein receptors (SNAREs) for vesicle fusion, is sufficient to generate stable, nonidentical compartments. A requirement for establishing and maintaining distinct compartments is that each coat preferentially packages certain SNAREs during vesicle budding. Vesicles fuse preferentially with the compartment that contains the highest concentration of cognate SNAREs, thus further increasing these SNAREs. The stable steady state is the result of a balance between this autocatalytic SNARE accumulation in a compartment and the distribution of SNAREs between compartments by vesicle budding. The resulting nonhomogeneous SNARE distribution generates coat-specific vesicle fluxes that determine the size of compartments. With nonidentical compartments established in this way, the localization and cellular transport of cargo proteins can be explained simply by their affinity for coats.     

Pressure change and gas mixing induced by oscillations in a closed system

In an attempt to delineate some mechanical behaviors found in branching airways, pressure transmission, gas motion, and mixing were studied during high-frequency oscillation (HFO) in an idealized system consisting of a large straight tube and a rigid sphere linked together by a small straight tube. Depending on the frequency f, and on the unsteadiness dimensionless parameter alpha, pressure amplitude in the large tube is either strongly attenuated or amplified in the sphere. This finding may provide a theoretical basis for the pressure resonance phenomenon observed in the lung by previous investigators. Gas compression in the closed volume causes convective mixing throughout the system. The measured dispersion was found to be proportional to f(VT/A)2, in agreement with a recent report. However, bulk convective mixing was sufficient to explain the dispersion for oscillatory volumes (VT) as small as 80 percent of the small tube volume, as has been previously suggested.     

Electron transport chain in a thermotolerant yeast

Yeasts capable of growing and surviving at high temperatures are regarded as thermotolerant. For appropriate functioning of cellular processes and cell survival, the maintenance of an optimal redox state is critical of reducing and oxidizing species. We studied mitochondrial functions of the thermotolerant Kluyveromyces marxianus SLP1 and the mesophilic OFF1 yeasts, through the evaluation of its mitochondrial membrane potential (ΔΨ_m), ATPase activity, electron transport chain (ETC) activities, alternative oxidase activity, lipid peroxidation. Mitochondrial membrane potential and the cytoplasmic free Ca²⁺ ions (Ca²⁺ cyt) increased in the SLP1 yeast when exposed to high temperature, compared with the mesophilic yeast OFF1. ATPase activity in the mesophilic yeast diminished 80% when exposed to 40° while the thermotolerant SLP1 showed no change, despite an increase in the mitochondrial lipid peroxidation. The SLP1 thermotolerant yeast exposed to high temperature showed a diminution of 33% of the oxygen consumption in state 4. The uncoupled state 3 of oxygen consumption did not change in the mesophilic yeast when it had an increase of temperature, whereas in the thermotolerant SLP1 yeast resulted in an increase of 2.5 times when yeast were grown at 30^o, while a decrease of 51% was observed when it was exposed to high temperature. The activities of the ETC complexes were diminished in the SLP1 when exposed to high temperature, but also it was distinguished an alternative oxidase activity. Our results suggest that the mitochondria state, particularly ETC state, is an important characteristic of the thermotolerance of the SLP1 yeast strain.     

Vacuolar pH oscillations in mesophyll cells accompany oscillations of photosynthesis in leaves: Interdependence of cellular compartments,and regulation of electron flow in photosynthesis

Oscillations of photosynthesis induced in leaves of Vicia faba L. were accompanied by oscillations not only in the pH of the chloroplast stroma, but also by pH oscillations in the cytosol and in the vacuole of leaf mesophyll cells. Cytosolic pH oscillations were in phase with stromal oscillations, but antiparallel to vacuolar pH oscillations. During maxima of photosynthesis, the cytosolic pH exhibited maxima and the vacuolar pH minima. Vacuolar acidification is interpreted to be the result of energized proton transport from the cytosol into the vacuole. Since the ratio of dihydroxyacetone phosphate to phosphoglycerate is maximal during the peaks of photosynthesis (Stitt et al., 1988, J. Plant Physiol. 133, 133–143; Laisk et al., 1991, Planta 185, 554–562), while the activity of NADP-malic dehydrogenase is highest during minima of photosynthesis (Scheibe and Stitt, 1988, Plant Physiol. Biochem. 26, 473–481), the present data indicate in agreement with earlier observations (Yin et al., 1991, Planta 184, 30–34) that light-dependent cytosolic energization is brought about by the oxidation of dihydroxyacetone phosphate rather than of malate. They also indicate that the over-reduction of the electrontransport chain observed during minima of photosynthesis is relieved not predominantly by oxaloacetate reduction and export of the resulting malate from the chloroplasts but by another reaction, presumably oxygen reduction.Abbreviations CDCF 5-(and 6-)carboxy-2,7-dichlorofluorescein     

The plasmid prophage N15: a linear DNA with covalently closed ends

Coliphage N15 is a temperate bacteriophage whose prophage is a linear plasmid molecule with covalently closed ends (telomeres). The N15 prophage provided the first example of such DNA in prokaryotes and, up to now, it is the only known example of a linear plasmid in Escherichia coli. The linear N15 mature phage DNA has single-stranded cohesive ends. The phage and plasmid prophage DNAs are circularly permuted. The nucleotide structure of the telomere-forming site tel RL in phage DNA corresponds to the structures of the terminal hairpin loops. It suggests a unique mechanism for conversion of the circular phage DNA to the linear plasmid form, which is performed by the prokaryotic telomerase (protelomerase). The results of a comparison of the protelomerase with integrases lead us to suggest that these proteins may have evolved from a common ancestor. The mechanism of plasmid N15 replication is unknown. We propose that the protelomerase participates in linear plasmid replication, acting as a resolvase of replicative intermediates that are tail-to-tail linear dimers. The sequence analysis of the N15 DNA showed that it represents an evolutionary 'link' between plasmids F, P1, P4 and lambdoid bacteriophages.     

Effect of thallium on enzyme activity and unidirectional sodium transport in frog skin

The cytophotometric analysis of enzyme activity in the frog skin epithelium has shown that Tl+ accumulated by cells at millimolar concentrations causes a 70-80% inhibition of both succinate and alpha-ketoglutarate dehydrogenases, while the activity of Na, K-ATPase decreased only slightly. The opposite situation was true for the ouabain treatment. The accumulation of Tl+ by frog skin caused a substantial swelling of mitochondria. It is suggested that the earlier observed inhibition of the unidirectional Na+ transport by Tl+ might be resulted from a blocking of oxidative metabolism. The same cells poisoned by Tl+ were able to maintain their ion composition presumably at the expense of glycolysis.     

Gene flow and genetic structure of the aquatic macrophyte Sparganium emersum in a linear unidirectional river

1. River systems offer special environments for the dispersal of aquatic plants because of the unidirectional (downstream) flow and linear arrangement of suitable habitats.
2. To examine the effect of this flow on microevolutionary processes in the unbranched bur-reed ( Sparganium emersum ) we studied the genetic variation within and among nine (sub)populations along a 103 km stretch of the Niers River (Germany–The Netherlands), using amplified fragment length polymorphisms.
3. Genetic diversity in S. emersum populations increased significantly downstream, suggesting an effect of flow on the pattern of intrapopulation genetic diversity.
4. Gene flow in the Niers River is asymmetrically bidirectional, with gene flow being approximately 3.5 times higher in a downstream direction. The observed asymmetry is probably caused by frequent hydrochoric dispersal towards downstream locations on the one hand, and sporadic zoochoric dispersal in an upstream direction on the other. The spread of vegetative propagules (leaf and stem fragments) is probably not an important mode of dispersal for S. emersum , suggesting that gene flow is mainly via seed dispersal. Realized dispersal distances exceeded 60 km, revealing a potential for long-distance dispersal in S. emersum .
5. There was no correlation between geographical and genetic distances among the nine S. emersum populations (i.e. no isolation by distance), which may be due to the occurrence of long-distance dispersal and/or colonization and extinction dynamics in the Niers River.
6. Overall, the genetic population structure and regional dispersal patterns of S. emersum in the Niers River are best explained by a linear metapopulation model. Our study shows that flow can exert a strong influence on population genetic processes of plants inhabiting stream systems.     

A mathematical model of oxygen transport in intact muscle with imposed surface oscillations

A one-dimensional (1D) reaction-diffusion equation is presented to model oxygen delivery by the microcirculation and oxygen diffusion and consumption in intact muscle. This model is motivated by in vivo experiments in which oscillatory boundary conditions are used to study the mechanisms of local blood flow regulation in response to changes in the tissue oxygen environment. An exact periodic solution is presented for the 1D 'in vivo' model and shown to agree with experimental data for the case where the blood flow regulation system is not activated. Approximate low- and high-frequency solutions are presented, and the latter is shown to agree with the pure diffusion solution in the absence of sources or sinks. For the low frequencies considered experimentally, the 1D in vivo model shows that as depth increases: (i) the mean of tissue O(2) oscillations changes exponentially, (ii) the amplitude of oscillations decreases very rapidly, and (iii) the phase of oscillations remains nearly the same as that of the imposed surface oscillations. The 1D in vivo model also shows that the dependence on depth of the mean, amplitude, and phase of tissue O(2) oscillations is nearly the same for all stimulation periods >30s, implying that experimentally varying the forcing period in this range will not change the spatial distribution of the O(2) stimulation.     

Statistical theory of chain scission and concurrent damage not associated with chain scission in linear polymers

A statistical theory of the parallel accumulation of randomly placed breaks and damage not associated with breaks in linear polymers is presented. Expressions for the weight fraction of polymer in the form of chains that bear n or more sites of nonbreak damage (markers) are developed, and results of numerical computations with them presented. The effects of polydispersity in the undamaged sample are discussed. The relation of the computed quantities to experimental methods used in the study of damage to nucleic acids due to radiation and chemical exposure is discussed.     

Isotropic sequence order learning using a novel linear algorithm in a closed loop behavioural system

In this article, we present an isotropic algorithm for sequence order learning. Its central goal is to learn the causal relation between two (or more) inputs in order to react to the earliest incoming signal after successful learning (like in typical classical conditioning situations). We implement this algorithm in a behaving system (a robot) thereby creating a closed loop situation where the learner's actions influence its own sensor inputs to the end of creating an autonomous agent. Autonomous behaviour implies that learning goals are internally defined within the organism's capabilities. Standard learning models for sequence learning (e.g. temporal difference (TD)-learning) need an externally defined reward. This, however, is in conflict with the requirement of an implicitly defined internal goal in autonomous behaviour. Therefore, in this study we present a system in which the external reward is replaced by a reflex loop. This loop explicitly includes the environment. Every reflex loop has the inherent disadvantage, which is that its re-actions occur each time just after a reflex-eliciting sensor event and thus 'too late'. However, a reflex can serve as the internal reference for sequence order learning, which has the task of eliminating this disadvantage by creating earlier anticipatory actions. In our system learning is achieved by modifying synaptic weights of a linear neuron with a correlation based learning rule which involves the derivative of the neuron's output. All input lines are entirely isotropic. The synaptic weight change curve of this rule is strongly related to the temporal Hebb learning rule, which was found in spike timing experiments. We find that after learning the reflex loop is replaced in functional terms with an earlier anticipatory action (and pathway). In addition, we observed that the synaptic weights stabilise as soon as the reflex remains silent.     

Review of research on closed loop supply chain management in the process industry

Closed loop supply chain (CLSC) management is a major enabler for sustainability in value creating networks. This contribution aims to describe and analyze the main characteristics of CLSC planning in the process industry and the related publications, in order to determine the evolution and gaps of this current research over time and improve our understanding of this issue. We built up a database with the articles on CLSC in different sectors of the process industry and identified the most relevant journals within this field. Furthermore, we derive and identify the requirements for CLSC considerations in the process industry for verifying whether these requirements are met in the literature so far. In addition, we have explored the topic, the methodology and the techniques of analysis, as well as other relevant aspects of the research in this field. We mainly focus on general and specific quantitative approaches, observing what has been done and how, where and by whom it has been carried out. The result is an extensive review of the research work itself and their limitations having an influence on CLSC concepts for the process industry. We conclude with some suggestions to those who begin to research on this apparently disregarded topic.     

Heterogeneity of membrane transport quantified by the analysis of a unidirectional flux transient of charged tracer

A planar mosaic membrane consists of patches, each with a given area, diffusion coefficient, and mobility of charged tracer; a common electric field, constant in space and time, lies across all the patches. Given the properties of the patches, the transient of the total unidirectional flux (summed over the patches) is predictable. Here we deal with the inverse problem: Given only the observed transient of the total unidirectional flux (as defined experimentally by Ussing), the unknown transport heterogeneity of the mosaic membrane is to be analyzed. Results obtained previously for uncharged tracers are generalized to include effects of the field. In particular, the ratio of the arithmetic and harmonic means (both area-weighted) of the diffusion coefficients, evaluated over the membrane, is expressed in terms of only the observed transient and the field strength and is used to characterize the heterogeneity; and the unique exact solution of the inverse problem for two kinds of patches is recovered at any field strength. If the mosaic consists of n distinct kinds of patches, a sweep of the field strength from low to high values reveals (at most) n steplike shapes in the time course of the total unidirectional flux (normalized to its final steady value), which permit an approximate analysis of the heterogeneity by elementary means.     

High allozyme diversity and unidirectional linear migration patterns within a population of tetraploid Isoetes sinensis, a rare and endangered pteridophyte

Isoetes sinensis (Isoetaceae), an aquatic quillwort which occurs only in two fragmented sites of China as an allotetraploid, is critically endangered. Genetic variation among eight subpopulations of I. sinensis was examined in the Xin’an River (119°14′–15′E, 29°28′N) by using allozyme polymorphism. Eighteen loci of 10 enzyme systems were examined and used for the analysis of population genetic parameters. As expected for allotetraploids, fixed heterozygosity was found at four loci. A high level of genetic diversity was observed in the population, with mean number of alleles per loci of 1.8, and mean percentage of polymorphic loci of 55.6%, which were much higher than the average values in fern species. The genetic variation within each subpopulation was not positively correlated with its size, which may be explained by high gene flow (Nm = 2.57), clonal reproduction and fixed heterozygosity of allopolyploid. The I. sinensis population contained high clonal diversity (PD = 0.39, D = 0.95), indicating the successful seedling recruitment of the population. Significant positive relationship was detected between clonal diversity and the size of subpopulation. Partitioning the genetic diversity indicated that 91.1% of the genetic variation was within subpopulations and only 8.9% existed among subpopulations. The migration pattern of I. sinensis along the Xin’an River is best explained by a source–sink model, but with unidirectional gene flow among subpopulations underlined by hydrochoric force. The results were then discussed in relation to both in situ and ex situ conservation efforts of the population.     

A gadolinium(III) nitronyl nitroxide linear chain with a complex spin structure

A new nitronyl nitroxide radical, 2-(4-carboxy-phenyl)-4,4,5,5-tetra-methyl-4,5-dihydro-1H-imidazol-1-oxyl-3-oxide, was used to prepare a linear chain system containing Gd(II) ions and these radicals. With this radical which has two sets of coordinating oxygen atoms, it was possible to build a very peculiar spin system with a complex magnetic structure.