A generalized diffusion model for growth and dispersal in a population

A reaction-diffusion model is presented in which spatial structure is maintained by means of a diffusive mechanism more general than classical Fickian diffusion. This generalized diffusion takes into account the diffusive gradient (or gradient energy) necessary to maintain a pattern even in a single diffusing species. The approach is based on a Landau-Ginzburg free energy model. A problem involving simple logistic kinetics is fully analyzed, and a nonlinear stability analysis based on a multi-scale perturbation method shows bifurcation to non-uniform states.Part of this work was done while at the Mathematical Institute, Oxford University as a Senior Visiting Fellow supported by the Science Research Council of Great Britain under grant GR/B31378     

Analysis of structural similarities between brain Thy-1 antigen and immunoglobulin domains. Evidence for an evolutionary relationship and a hypothesis for its functional significance.

The Thy-1 membrane glycoprotein from rat brain is shown to have structural and sequence homologies with immunoglobulin (Ig) domains on the basis of the following evidence. 1. The two disulphide bonds of Thy-1 are both consistent with the Ig-fold. 2. The molecule contains extensive beta-structure as shown by the c.d. spectrum. 3. Secondary structure prediction locates beta-strands along the sequence in a manner consistent with the Ig-fold. 4. On the basis of rules derived from known beta-sheet structures, a three-dimensional structure with the Ig-fold is predicted as favourable for Thy-1. 5. Sequences in the proposed beta-strands of Thy-1 and known beta-strands of Ig domains show significant sequence homology. This homology is statistically more significant than for the comparison of proposed beta-strand sequences of beta 2-microglobulin with Ig domains. An hypothesis is presented for the possible functional significance of an evolutionary relationship between Thy-1 and Ig. It is suggested that both Thy-1 and Ig evolved from primitive molecules, with an Ig fold, which mediated cell--cell interactions. The present-day role of Thy-1 may be similar to that of the primitive domain.     

Degradation patterns and intermediates in the anaerobic digestion of glucose: Experiments with 14C-labeled substrates

A mineral salts medium containing 1% (w/v) glucose was subjected to anaerobic digestion in an upflow reactor. Performance with respect to utilization of glucose was monitored by collection of fermentation gases and calculation of carbon mass balances. Sub-samples of bacterial supennsions from the upflow reactor were incubated with (U-¹⁴C)-glucose, (U-¹⁴C)-acetate, (2-¹⁴C)-propionate, (1-¹⁴C)-butyrate or ¹⁴C-carbonate. Individual radioactive products in samples from incubation mixtures were analysed by radio gas chromatography.Quantitatively, acetate and propionate were the only important intermediates in glucose degradation by glucose-adapted sludge, with acetate accounting for the largest part of intermediary fatty acid flux.Abbreviations used ATP Adenosine Triphosphate - TIC Total Inorganic Carbon - TOC Total Organic Carbon - VFA Volatile Fatty Acids The research described in this publication was supported by the Dutch Ministry of Public Health and Environmental Protection.     

Study of storage iron in cultured chick embryo fibroblasts and rat glioma cells, using M?ssbauer spectroscopy

57Fe M?ssbauer spectra of normal and Rous sarcoma virus-infected cultured chick embryo fibroblasts and rat glioma cells have been measured between 0.08 and 318 K. Ferritin-like iron and bacterio-ferritin-like iron have been found in these cells, in various relative amounts, indicating a close relationship between the two storage materials. The bacterio-ferritin-like iron was found to be predominantly membrane-bound. Above 260 K very wide lines were observed in the M?ssbauer spectra, yielding an effective viscosity of about 1 poise in the normal chick embryo fibroblasts and about 0.5 poise in the virus-infected chick embryo fibroblasts.     

The mevalonate pathway in the bloodstream form of Trypanosoma brucei. Identification of dolichols containing 11 and 12 isoprene residues

The major surface antigen of the bloodstream form of Trypanosoma brucei, the variant surface glycoprotein, is attached to the plasma membrane via a glycosylphosphatidylinositol anchor. The biosynthesis of the glycosylphosphatidylinositol anchor, as well as the assembly of the asparagine-linked oligosaccharide chains found on the variant surface glycoproteins, involves polyisoprenoid lipids that act as sugar carriers. Preliminary observations (Menon, A.K., Schwarz, R.T., Mayor, and Cross, G.A.M. (1990) J. Biol. Chem. 265, 9033-9042) suggested that the sugar carriers in T. brucei were short-chain polyisoprenoids containing substantially fewer isoprene residues than polyisoprenols in mammalian cells. In this paper we describe metabolic labeling experiments with [3H]mevalonate, as well as chromatographic and mass spectrometric analyses of products of the mevalonate pathway in T. brucei. We report that cells of the bloodstream form of T. brucei contain a limited spectrum of short chain dolichols and dolichol phosphates (11 and 12 isoprene residues). The total dolichol content was estimated to be 0.28 nmol/10(9) cells; the dolichyl phosphate content was 0.07 nmol/10(9) cells. The same spectrum of dolichol chain lengths was also found in a polar lipid that could be labeled with [3H]mevalonate, [3H]glucosamine, and [3H]mannose, and which was characterized as Man5GlcNAc2-PP-dolichol. The most abundant product of the mevalonate pathway identified in T. brucei was cholesterol (140 nmol/10(9) cells). Ubiquinone (0.09 nmol/10(9) cells) with a solanesol side chain was also identified.     

Analysis of protease-sensitive regions in the skeletal muscle sodium channel in vitro and implications for channel tertiary structure.

The tertiary structure of the rat skeletal muscle sodium channel was probed in vitro by determining regions of sensitivity to V-8 protease, trypsin, and chymotrypsin. Resultant channel fragments were identified with antibodies to defined sequences distributed along the primary structure. The temporal pattern of proteolysis was followed with channel protein in either detergent-phospholipid micelles or membrane fragments as well as with channel exposed to sodium dodecyl sulfate. Proteolysis in micelles and membranes occurred in discrete, reproducible steps that were similar in both systems. Although the size of intermediates varied slightly, their sequence of appearance was similar for all enzymes, suggesting that the observed pattern was determined by the relative accessibility of selected sites in the tertiary structure. No major change in channel organization appeared to occur after solubilization of membranes in nonionic detergents. Highly accessible sites in the native structure included the carboxyl terminus and the region linking the second and third internal repeat domains, while the amino terminus and the repeat domains themselves were relatively resistant to proteolysis unless the protein was denatured. Kinetically, interdomain II-III was the most readily cleaved; interdomains I-II and especially III-IV were less easily accessible. While domains I and IV appeared to remain intact throughout our experiments, limit fragments for epitopes associated with domains II and III suggest that cleavage eventually occurs at sites between the putative S5 and S6 helices in these domains.