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PubMed2002

Chlamydomonas, a model system for studying the assembly and dynamics of photosynthetic complexes.

The green unicellular alga Chlamydomonas reinhardtii has emerged as a powerful model system for studying the biosynthesis of the photosynthetic apparatus and the acclimation of this system to changes in light conditions. The assembly of the photosynthetic complexes involves the coordinate interaction between the nuclear and chloroplast genetic systems. Many factors involved in specific chloroplast post-transcriptional steps have been identified and characterized. Chlamydomonas is able to adapt to changes in light quality and in cellular ATP content by performing state transition, a process that leads to a redistribution of light excitation energy between photosystem II and photosystem I and that involves the redox state of the plastoquinone pool, the cytochrome b(6)f complex and one or several kinases specific for the light-harvesting system. Genetic approaches have provided new insights into this process.

Adaptation, Physiological↗
PubMed2002

Degradation of the Amadori compound N-(1-deoxy-D-fructos-1-yl)glycine in aqueous model systems.

The fate of the Amadori compound N-(1-deoxy-D-fructos-1-yl)glycine (DFG) was studied in aqueous model systems as a function of time and pH. The samples were reacted at 90 degrees C for up to 7 h while maintaining the pH constant at 5, 6, 7, or 8. Special attention was paid to the effect of phosphate on the formation of glycine and the parent sugars glucose and mannose, as well as formic and acetic acid. These compounds and DFG were quantified by high-performance anion-exchange chromatography. The rate of DFG degradation increased with pH. Addition of phosphate accelerated this reaction, particularly at pH 5-7. The rate of glycine formation increased with pH in both the absence and presence of phosphate. High glycine concentrations (60-70 mol %) were obtained, preferably at pH 6-8 with phosphate. However, the yield of glycine formed from DFG decreased at the advanced reaction stage for all pH values studied, both in water and in phosphate buffer. The rate of parent sugar formation increased from pH 5 to pH 7 in the absence of phosphate, leading to glucose and mannose in a constant ratio of 7:3. Addition of phosphate accelerated this reaction, yielding up to 18% parent sugars, most likely formed by reverse Amadori rearrangement. The formation rate of acetic and formic acid increased with increasing pH. The sum of both acids attained 76 mol %. However, the acetic acid concentrations were much higher than those of formic acid.

Acetic Acid↗
PubMed2002

The Baltic Sea as a model system for studying postglacial colonization and ecological differentiation, exemplified by the red alga Ceramium tenuicorne.

The Baltic Sea provides a unique model system for studying genetic effects of postglacial colonization and ecological differentiation, because all marine organisms must have immigrated after the opening of the Danish Straits 8000 years ago and responded to the development of the steep Skagerrak-Baltic salinity gradient. The red alga Ceramium tenuicorne shows conspicuous variation in growth and reproduction along this gradient. Herein we obtained reproductive data coupled with two types of molecular markers, one organellar (cox2-3 spacer sequences of mitochondrial DNA; mtDNA) and one mainly nuclear (random amplified polymorphic DNAs; RAPDs). Nine main populations were sampled in a nested spatial hierarchy including three salinity regions (Oslofjorden, Kattegat, and the Baltic Sea), and nine additional populations were sampled for the mtDNA analysis. Asexuality was frequent at low (Baltic) and medium (Kattegat) salinities but virtually absent at the highest salinity (Oslofjorden). Five mtDNA haplotypes were observed, of which two highly divergent ones were common. One was restricted to and fixed in Oslofjorden, and the other, which was closely related to the three rare haplotypes, was found from southernmost Norway via Kattegat into the Baltic. The RAPD data revealed, on the other hand, a continuous cline corresponding to the salinity gradient, with 27.4% divergence among salinity regions and most of the variation stored at the smallest spatial scale analysed (64.2%; within 1 m2 subpopulations). The combined data suggest colonization from a diverse Atlantic glacial gene pool followed by (1) lineage sorting of ancestral mtDNA polymorphisms and (2) strong differential selection among nuclear genotypes along the salinity gradient, including selection for nonrecombinant multiplication of those best fit to the marginal low-salinity habitats.

Adaptation, Physiological↗
PubMed1990

[Phenylketonuria as a model system for DNA diagnosis of hereditary disorders].

Phenylketonuria (PKU), due to a defect in phenylalanine hydroxylase (PAH), is presented as a model system for computer-aided DNA diagnosis of genetic diseases. Eight different restriction fragment length polymorphism (RFLP) markers have been localized within the introns of the 90 kb PAH gene (located on chromosome 12). These RFLPs can be combined in 384 different ways and each combination has been defined as a particular haplotype. A special computer program has been developed to calculate the possible haplotype combinations in a PKU core family (index patient and parents), with the goal to derive unambiguously both the PAH and PKU alleles. Taking into account that participation of other members of the family (grandparents or brothers/sisters) is sometimes necessary, haplotyping by itself is sufficient to establish (or exclude) the PKU status of an individual in approximately eight out of ten PKU families.

Chromosomes, Human, Pair 12↗
PubMed2002

Continuous system modeling of equilibrium dialysis for determinations of tissue partitioning of parathion and paraoxon.

A tissue/blood partition coefficient, defined as the ratio of tissue chemical concentration to that of the venous outflow of the tissue when at equilibrium, is an important parameter required for physiological based pharmacokinetic models. While many techniques have been developed to quantify tissue/blood partition coefficients for various chemicals, there is no single best approach for their determination. In the current study, equilibrium dialysis of the organophosphorus insecticide parathion and its active metabolite paraoxon was undertaken to assess their partitioning into rat liver. A mass balance analysis of the contents of the dialysis cells suggested that significant levels of parathion and paraoxon were bound to the dialysis membranes. There was no evidence of metabolism of either parathion or paraoxon by the very dilute liver homogenate utilized in the dialysis. In order to investigate the potential impact of binding of a chemical to dialysis membrane during determination of partition coefficients, a computer model of a dialysis system was constructed. The model assumed that all processes occurring within the dialysis cell were first or second order in nature, and that binding to the dialysis membrane occurred symmetrically on both sides of the membrane. Variations in the total number of simulated binding sites on dialysis membrane revealed that increasing the degree of membrane binding resulted in decreased compound on the homogenate and buffer sides of the dialysis cells. However, the final tissue/buffer partition coefficient was unaffected by these alterations in membrane binding, although increased membrane binding prolonged the incubation time required to achieve equilibrium. These simulations suggest that loss of a compound to membrane binding does not preclude the use of equilibrium dialysis for determination of tissue/buffer, and therefore tissue/blood, partition coefficients, provided the dialysis system is allowed to proceed to equilibrium.

Algorithms↗
PubMed1990

Caenorhabditis elegans: a new model system for the study of learning and memory.

The extensive information on the neuroanatomy, development and genetics of Caenorhabditis (C.) elegans make it an ideal candidate model system for the analysis of the mechanisms underlying learning and memory. A first step in this analysis is the demonstration of the capacity of C. elegans to learn. In these experiments non-associative learning in C. elegans was investigated by observing changes in reversal reflex response amplitude to a mechanical vibratory stimulus. The results from these studies of non-associative learning show that C. elegans is capable of short-term habituation, dishabituation and sensitization, as well as long-term retention of habituation training lasting for at least 24 h. These findings set the stage for detailed developmental, genetic and physiological analyses of learning and memory.

Animals↗
PubMed1980

Quantitative aspects of the cytochemical demonstration of glucose-6-phosphate dehydrogenase with tetranitro BT studied in a model system of polyacrylamide films.

The cytochemical determination of the activity of glucose-6-phosphate dehydrogenase (G6PDH) with tetranitro blue tetrazolium (TNBT) was studied with model films of polyacrylamide gel incorporating purified enzyme. This model system enabled a quantitative study to be made of different parameters involved with the cytochemical assay as it is applied to sections or smears. The enzyme activity of G6PDH incorporated in the model films was also assayed biochemically. Optimal conditions for retaining the maximum amount of enzymic activity are described. The behaviour of G6PDH towards enzyme inhibitors was found to be similar in model films and in solution. WIth TNBT, absorbance measurements at a single wavelength (535 nm) were used to estimate the enzyme activity quantitatively. When carried out under standardized conditions, both the cytochemical and biochemical assay showed a linear relation with the time of incubation and obeyed the Beer-Lambert law. The correlation between biochemical and cytochemical data was very high, which enabled cytochemical data to be converted into absolute units of enzyme activity. The data obtained in this way closely resembled the data of enzyme activity calculated from the absorbance of formazan produced inside polyacrylamide model films and afterwards extracted into a suitable solvent.

Acrylamides↗
PubMed2000

Medakafish as a model system for vertebrate developmental genetics.

Several teleosts, such as the zebrafish and the medakafish or medaka (Oryzias latipes), are used as vertebrate model systems in various fields of biology. The medaka is suitable for use in genomic studies because of its small genome size. Moreover, our recent results of small-scale mutagenesis in the medaka indicate that it is possible to identify mutations, the phenotypes of which could not be found in zebrafish mutants obtained by large-scale mutagenesis. An example is Oot (One-sided optic tectum), a maternal-effect mutation. In the Oot phenotype, bilateral symmetry is broken in the optic tectum in the early developmental stages, and either the left or right morphology is duplicated on both sides. Medaka inbred strains can be produced and used to study quantitative traits in vertebrate development. Data presented support the use of medaka as another important fish model for the study of vertebrate developmental genetics.

Animals↗
PubMed2004

Are natural microcosms useful model systems for ecology?

Several recent, high-impact ecological studies feature natural microcosms as tools for testing effects of fragmentation, metacommunity theory or links between biodiversity and ecosystem processes. These studies combine the microcosm advantages of small size, short generation times, contained structure and hierarchical spatial arrangement with advantages of field studies: natural environmental variance, 'openness' and realistic species combinations with shared evolutionary histories. This enables tests of theory pertaining to spatial and temporal dynamics, for example, the effects of neighboring communities on local diversity, or the effects of biodiversity on ecosystem function. Using examples, we comment on the position of natural microcosms in the roster of ecological research strategies and tools. We conclude that natural microcosms are as versatile as artificial microcosms, but as complex and biologically realistic as other natural systems. Research to date combined with inherent attributes of natural microcosms make them strong candidate model systems for ecology.

Journal Article↗
PubMed1985

The Neuman Systems Model in practice. Planning phase.

How do you choose and plan for the implementation of a conceptual model for professional nursing practice? This article discusses one institution's experience with the Neuman Systems Model. The process discussed in this article will serve as a guide for other nursing administrators considering this significant undertaking.

Curriculum↗
PubMed2000

Evaluation of boar sperm as a model system to study the mechanism of spermicidal activity of vanadocenes.

bis-cyclopentadienyl [Cp] complexes of vanadium(IV) or vanadocenes are rapid and potent inhibitors of human sperm motility with potential as a new class of contraceptive agents. We investigated the utility of boar sperm as a model system to study the mechanisms of drug action because boar sperm lacks phosphocreatine and creatine kinase activity, the essential components of the "phosphagen shuttle" system for human sperm motility. Two representative vanadocenes, vanadocene dichloride [VDC] and bis[pentamethylcyclopentadienyl] vanadium dichloride [VPMDC], in which the bis-Cp rings were substituted with five electron-donating methyl groups were evaluated. The concentration-dependent effects of VDC and VPMDC on spermicidal activity, axonemal dynein adenosine triphosphatase (ATPase) activity, and tyrosine phosphorylation of global sperm proteins were assessed by computer-assisted sperm analysis, spectrophotometry, and immunoblotting, respectively. Both the unsubstituted and the pentamethyl-substituted vanadocene induced rapid sperm immobilization (T(1/2) < 15 s). Substitution of the bis-Cp rings by five methyl groups augmented the SIA of VDC threefold. The EC(50) values for VDC and VPMDC were 2.1 and 0.76 microM, respectively. Spermicidal activity of vanadocenes was not associated with the inhibition of dynein ATPase(s) or increase in tyrosine phosphorylation of sperm proteins. These results suggest that the potent spermicidal activity of vanadocenes against boar sperm is mediated by a unique mechanism that is independent of dynein ATPase activity, phosphatase activity, and phosphocreatine/creatine kinase system. Therefore, boar sperm is a suitable model for further investigating the molecular mechanism of spermicidal action of vanadocenes.

Animals↗
PubMed2000

Progress of the Maillard reaction and antioxidant action of Maillard reaction products in preheated model systems during storage.

The progress of the Maillard reaction and the effect of Maillard reaction products (MRPs) on lipid oxidation in preheated model systems containing pregelatinized starch, glucose, lysine, and soybean oil have been studied during storage. The samples, either containing all components or excluding one or more of them, were heated at 100 degrees C for 90 min and then stored for up to 180 days at 25 degrees C. Browning indices and lipid oxidation were measured, and the results showed that, in samples containing oil, the Maillard reaction had a significant rate also at room temperature and confirmed the ability of MRPs to retard peroxide formation. Under the conditions adopted the rate of the Maillard reaction was increased by the presence of the oil and its oxidation products. The antioxidant action of the MRPs was also evaluated using a peroxide scavenging test based on crocin bleaching. The results demonstrated that antioxidant activity developed with increased browning of the samples.

Antioxidants↗
PubMed1993

Use of chaos theory and complex systems modeling to study alcohol effects on fetal condition.

A systems dynamics computer model to predict birth complications for individual pregnant woman was developed from prospectively conducted data on a database of 125 pregnant women. The model is based upon nonlinear mathematics derived from the study of chaos and complex systems. The model was then tested prospectively on 27 additional pregnant women, making predictions on their level of obstetrical risk. The model was refined until it correctly predicted the outcomes of all 125 cases in the development database. Prediction was made with an accuracy of 25/27 cases for the prospective test cases. Predictions were made for fetal condition at birth, presence or absence of operative delivery, and presence or absence of uterine dysfunction. Then the model was used to explore alcohol use during pregnancy. A reasonable spread of alcohol use existed among subjects, allowing consideration of alcohol effects. Alcohol was found to have differential effects on fetal condition at birth depending upon the presence or absence of high levels of psychosocial stress and the use of other substances. In all cases, the effect of alcohol was only evident after the 10 drinks per week level was reached. For the high-stress/one other substance group, there could be an 18-fold effect on fetal condition at birth. For the low-stress/one other substance group, the effect was only 3-fold, and for the alcohol alone group, the effect was negligible.

Alcohol Drinking↗
PubMed2003

Whey proteins as a model system for chromatographic separation of proteins.

Although chromatographic separation of whey proteins has been considered too expensive, whey may serve as an excellent model mixture to investigate and validate the use of simulation tools in the development and optimization of chromatographic separations and the outcome could easily be utilized since the model system has an intrinsic value. Besides, milk from transgenic animals could be an attractive source of pharmaceuticals which must be separated from the other proteins in the milk. Several whey proteins are of interest especially, alpha-lactalbumin, beta-lactoglobulins, immunoglobulins, lactoperoxidase, and lactoferrin. The scope of the project is to develop a consistent set of chromatographic data for whey proteins including isotherms, transport properties and scale-up studies and to develop the appropriate models for the anion exchangers Q-Sepharose XL, Source 30Q, Ceramic Q-HyperD F, and Merck Fractogel EMD TMAE 650 (S). In this work we have determined and correlated gradient and isocratic retention volumes in the linear range of the isotherm for alpha-lactalbumin, beta-lactoglobulin A and B, and bovine serum albumin at a pH from 6 to 9 at various NaCl concentrations.

Chromatography, Liquid↗
PubMed2001

Cavefish as a model system in evolutionary developmental biology.

The Mexican tetra Astyanax mexicanus has many of the favorable attributes that have made the zebrafish a model system in developmental biology. The existence of eyed surface (surface fish) and blind cave (cavefish) dwelling forms in Astyanax also provides an attractive system for studying the evolution of developmental mechanisms. The polarity of evolutionary changes and the environmental conditions leading to the cavefish phenotype are known with certainty, and several different cavefish populations have evolved constructive and regressive changes independently. The constructive changes include enhancement of the feeding apparatus (jaws, taste buds, and teeth) and the mechanosensory system of cranial neuromasts. The homeobox gene Prox 1, which is expressed in the expanded taste buds and cranial neuromasts, is one of the genes involved in the constructive changes in sensory organ development. The regressive changes include loss of pigmentation and eye degeneration. Although adult cavefish lack functional eyes, small eye primordia are formed during embryogenesis, which later arrest in development, degenerate, and sink into the orbit. Apoptosis and lens signaling to other eye parts, such as the cornea, iris, and retina, result in the arrest of eye development and ultimate optic degeneration. Accordingly, an eye with restored cornea, iris, and retinal photoreceptor cells is formed when a surface fish lens is transplanted into a cavefish optic cup, indicating that cavefish optic tissues have conserved the ability to respond to lens signaling. Genetic analysis indicates that multiple genes regulate eye degeneration, and molecular studies suggest that Pax6 may be one of the genes controlling cavefish eye degeneration. Further studies of the Astyanax system will contribute to our understanding of the evolution of developmental mechanisms in vertebrates.

Animals↗
PubMed2001

An efficient simulation method for discrete-value controlled large-scale neuromyoskeletal system models.

An efficient Euler-Adams hybrid integration scheme for simulating on the computer discrete-value controlled large-scale neuromyoskeletal system models is presented. If, as discussed in the model, the differential equations describing the recruitment and excitation dynamics of the muscular subsystem are independent of the corresponding contraction-dynamical state variables, they can be integrated separately over certain time intervals by a modified Euler routine that handles discontinuous right-hand sides efficiently. The resulting myostates can then be stored and used as continuous input values for the subsequent integration by an Adams predictor-corrector algorithm of the remaining contraction-dynamical and skeletomechanical state differential equations. With such an Euler-Adams hybrid integration routine one avoids the detrimental effects and efficiency losses associated with frequent stop-restart cycles of otherwise efficient Adams-type algorithms, which cycles are forced by discontinuities on the right-hand side of the myostate equations. In the example presented, a reduction in the execution time by a factor of about 5 could be achieved by implementing the proposed technique.

Algorithms↗
PubMed1995

Influence of amino acids on the formation of mutagenic/carcinogenic heterocyclic amines in a model system.

Mixtures of creatinine, glucose and various single amino acids were heated at 180 degrees C for 10 min in an aqueous model system. The heated mixtures all showed mutagenic activity, ranging from 80 to 2400 TA98 revertant colonies/mumol creatinine with metabolic activation. Testing of HPLC fractions for mutagenic activity showed each mixture to contain several mutagenic components, some of which corresponded to known heterocyclic amines and others to unknown compounds. The presence of 2-amino-3-methyl-imidazo[4,5-f]quinoxaline, 2-amino-3,8-dimethylmidazo[4,5-f]quinoxaline and 2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline in most of the samples was established using HPLC with photodiode array detection and liquid chromatography/mass spectrometry with electrospray interface and single ion monitoring. In addition, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline, 2-amino-1-methyl-6-phenylimidazo[4,5-f]quinoxaline, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole and 3-amino-1-methyl-5H-pyrido[4,3-b]indole and the co-mutagenic compounds 9H-pyrido[3,4-b]indole and 1-methyl-9H-pyrido[3,4-b]indole were detected in some samples.

Amines↗