Location and orientation relative to the micelle surface for glucagon in mixed micelles with dodecylphosphocholine EPR and NMR studies

The spin labels, 5-doxylstearate, 12-doxylstearate, 16-doxylstearate and 1-oxyl-2,2,6,6-tetramethyl-4-dodecylphospiperidine, have been incorporated into dodecylphospocholine micelles and mixed dodecylphosphocholine/ glucagon micelles. The EPR spectral parameters for the different spin labels and the ¹H- and ¹³C-NMR relaxation rates for nuclei of the detergent molecules indicated that inclusion of up to one spin label molecule per micelle had little influence on the spatial organization of the micelles. Furthermore, the location and environment of the spin labels in the dodecylphosphocholine micelles were not noticeably affected by the addition of glucagon and the ¹H-NMR spectra observed for glucagon in mixed spin label/deuterated dodecylphosphocholine/glucagon micelles showed that the different spin labels had essentially no effect on the conformation of glucagon. Approximate spatial locations within the micelle for the nitroxide moieties of the different spin labels were determined from the NMR relaxation rates observed for different nuclei of dodecylphosphocholine. On this basis, the line broadening of individually assigned glucagon ¹H-NMR lines by the different spin labels was used to determine the approximate orientation of the polypeptide chain with respect to the micelle surface. Overall, the data indicate that the glucagon backbone runs roughly parallel to the micelle surface, with the depth of immersion adjusted so that polar and apolar side chains can be oriented towards the surface or interior of the micelle, respectively.     

Lipoxygenbase-derived products of arachidonic acid mediate stimulation of hexose uptake in human polymorphonuclear leukocytes

The titration of metal-freed bovine α-lactalbumin with Mg²⁺ ions causes a two-stepped decrease in the tryptophan fluorescence quantum yield and a pronounced spectral shift towards shorter wavelengths, which seems to be a result of the binding of two magnesium ions to the protein molecule. The magnesium binding constants evaluated from the fluorimetric Mg²⁺-titration are 2·10³ and 2·10² M^?1. Mg²⁺ ions in millimolar concentrations almost do not influence the binding of Ca²⁺ ions to the protein.     

On the study of two interacting populations one of which acts independently of the other

Many ecological and biological systems can be studied in terms of a bivariate stochastic branching process, {X ₁ (t), X ₂ (t)}, each of whose components (or populations) varies in magnitude according to the laws of a generalized birth-death process. Of particular interest is such a model in which the birth and death rates of the first population,X ₁, are constant while those of the second population,X ₂, exhibit a functional dependence upon the magnitude of the first. It is shown, first, that the existence of the stochastic mean of a birth death process implies the existence of all higher moments. The values of all the factorial moments of such a process are then determined. The moments of the dependent population of the bivariate process are given in terms of its expectation and the joint probability density function of the process is determined. It is possible, therefore, to use Bayesian techniques to infer conclusions about the independent population, given information about the variation of the dependent one.     

A new species of Metacnephia Crosskey (Diptera: Simuliidae) from the south of England,with notes on its habitat and biology

Since the report of (Simulium) tredecimatum from “the stomach of a trout, England” no specimens of the genus Metacnephia have been reported from the British Isles. A full account of the morphological features of the larvae, pupae and adults of a new species, Metacnephia amphora is given together with a brief account of its larval growth and presence on a wide range of substrata in a small, temporary stream.     

Enzymatic elimination of substrates flowing through the intact liver

Enzymatic elimination of a class of substrates by the liver is analyzed in terms of a convective model of the microcirculation carrying the substrates. The elimination generates concentration gradients of the substrates which in turn affect the elimination rate through Michaelis-Menten saturation kinetics. The interplay of biochemical, anatomical and haemo-dynamic factors results in a variety of limiting regimes of elimination which are given a quantitative discussion and classification. The kinetic parameters of the enzymatic elimination reaction are expressed in terms of quantities observable on the intact liver. An overall elimination efficiency is defined by comparison with a homogenous process and evaluated for all elimination regimes, with clinical implications. Examples of two types of experiments supporting the validity of the model are presented.     

Stochastic processes in particle-number fluctuations in an electron-photon shower

The paper is concerned with the existence and asymptotic character of the nonlinear boundary value problemdG/dt=F(t,G,F, ¦α?β¦) (1) ¦α?β¦dF/dt=g(t,G,F, ¦α?β¦)G(o,¦α?β¦)=k ₁,G(∞,¦α?β¦)=k ₂ (2) as ¦α?β¦→ o+ The discussion is related to the problem of particle-number fluctuations in the theory of cosmic radiation andG andF denote respectively the probability generating functions for the electron distribution in an electron-initiated and a photon-initiated shower. A solution of the system (1) satisfying the boundary conditions (2) is constructed so that specified limiting conditions are fulfilled.     

Species specificity and intraspecific variation in the chemical profiles of Heliconius butterflies across a large geographic range

In many animals, mate choice is important for the maintenance of reproductive isolation between species. Traits important for mate choice and behavioral isolation are predicted to be under strong stabilizing selection within species; however, such traits can also exhibit variation at the population level driven by neutral and adaptive evolutionary processes. Here, we describe patterns of divergence among androconial and genital chemical profiles at inter‐ and intraspecific levels in mimetic Heliconius butterflies. Most variation in chemical bouquets was found between species, but there were also quantitative differences at the population level. We found a strong correlation between interspecific chemical and genetic divergence, but this correlation varied in intraspecific comparisons. We identified “indicator” compounds characteristic of particular species that included compounds already known to elicit a behavioral response, suggesting an approach for identification of candidate compounds for future behavioral studies in novel systems. Overall, the strong signal of species identity suggests a role for these compounds in species recognition, but with additional potentially neutral variation at the population level.     

New insights in the cellular processing of platinum antitumor compounds, using fluorophore-labeled platinum complexes and digital fluorescence microscopy

The cellular distribution and processing pathways of two platinum compounds, modeling the antitumor drug cisplatin (cDDP) in human osteosarcoma (U2-OS) cells is reported. A [Pt(en)Cl] entity has been covalently linked to a carboxyfluorescein diacetate (CFDA) moiety and to a dinitrophenyl (DNP) moiety. The two different constructs were administered to living cell cultures that were analyzed using digital fluorescence microscopy. The non-fluorescent CFDA construct becomes fluorescent after cellular uptake and subsequent acetate hydrolysis by esterases, and is therefore suitable to monitor platinum in living cells; the DNP construct can be visualized by immunocytochemistry and consequently serves as a control. Both complexes were readily internalized by the cells, and localized throughout the whole cell. After 2-3 h the complex accumulated in the nucleus, but 6-8 h after incubation a punctuate staining of a cytoplasmic region was observed, that persisted and became more pronounced after 24 h. The overall fluorescence in the cell decreased over time, implying a secretion of the platinum complex. Surprisingly, the accumulation remained visible after 72 h. Co-localization experiments with a Golgi apparatus-selective stain indicate the involvement of Golgi vesicles in intracellular processing of cisplatin-derived complexes. Immunocytochemical studies, using the DNP derivative, resulted in very similar images as obtained with the CFDA construct. CFDA-boc (a non-platinum-containing fluorescein derivative) was used as control: a faint staining throughout the whole cell was observed. Cisplatin-resistant U2-OS/Pt cells showed staining patterns very similar to the U2-OS cells using both platinum constructs. This study illustrates that only a very small portion of the platinum complex eventually remains bound to DNA, as after 24 h no significant fluorescence could be observed in the nucleus. Cisplatin-derived complexes with fluorescent tags afford a new insight into the cellular processing of these complexes and therefore may contribute to further unraveling of the mechanism of platinum antitumor complexes.     

Cultured gill epithelia as models for the freshwater fish gill

We review recent progress in the development of models for the freshwater teleost gill based on reconstructed flat epithelia grown on permeable filter supports in primary culture. Methods are available for single-seeded insert (SSI) preparations consisting of pavement cells (PVCs) only from trout and tilapia, and double-seeded insert (DSI) preparations from trout, containing both PVCs (85%) and mitochondria-rich cells (MRCs, 15%), as in the intact gill. While there are some quantitative differences, both SSI and DSI epithelia manifest electrical and passive permeability characteristics typical of intact gills and representative of very tight epithelia. Both preparations withstand apical freshwater exposure, exhibiting large increases in transepithelial resistance (TER), negative transepithelial potential (TEP), and low rates of ion loss, but there is only a small active apical-to-basolateral "influx" of Cl(-) (and not of Na(+)). Responses to various hormonal treatments are described (thyroid hormone T3, prolactin, and cortisol). Cortisol has the most marked effects, stimulating Na(+),K(+)-ATPase activity and promoting active Na(+) and Cl(-) influxes in DSI preparations, and raising TER and reducing passive ion effluxes in both epithelia via reductions in paracellular permeability. Experiments using DSI epithelia lacking Na(+) uptake demonstrate that both NH(3) and NH(4)(+) diffusion occur, but are not large enough to account for normal rates of branchial ammonia excretion, suggesting that Na(+)-linked carrier-mediated processes are important for ammonia excretion in vivo. Future research goals are suggested.