Tadpole shrimp structure macroinvertebrate communities in playa lake microcosms

Laboratory microcosms were used to assess whether tadpole shrimp, Triops sp., affect community structure of other native macroinvertebrates in playa lakes of the Southern High Plains of Texas. Removal of tadpole shrimp shortly after hatching reduced abundances of many taxa, and decreased subsequent taxonomic richness and diversity. For many invertebrates, the presence of tadpole shrimp in low numbers had a positive effect on mean abundance. Direct effects of tadpole shrimp include the reduction of prey species abundance, which in turn may alter biotic interactions among other taxa. Indirect effects include physical modification of the environment during foraging through surface sediments. Results suggest that tadpole shrimp may be a key species controlling structure of macroinvertebrate communities in playa lakes.     

Regulation of human erythrocyte glyceraldehyde-3-phosphate dehydrogenase by ferriprotoporphyrin IX

Erythrocyte glyceraldehyde-3-phosphate dehydrogenase (G3PD) is a glycolytic enzyme containing critical thiol groups and whose activity is reversibly inhibited by binding to the cell membrane. Here, we demonstrate that the insertion of ferriprotoporphyrin IX (FP) into the red cell membranes exerts two opposite effects on membrane bound G3PD. First, the enzyme is partially inactivated through oxidation of critical thiols. Dithiothreitol restores part of the activity, but some critical thiols are irreversibly oxidized or crosslinked to products of FP-induced lipid peroxidation. Second, G3PD binding to the membrane is modified and the enzyme is activated through displacement into the cytosol and/or release from its binding site.     

Miniaturization of absorbance assays using the fluorescent properties of white microplates

Miniaturization of high-throughput screening (HTS) assays has several obvious advantages, including increased throughput and lower cost by reduction in reagent consumption. Although absorbance assays are widely used in research laboratories, their application for HTS in a low-volume format has been met with mixed success because they are difficult to miniaturize. Challenges for the miniaturization of absorbance assays include low signal due to short path lengths and meniscus distortions in small well sizes. Here we describe a method to miniaturize absorbance assays to standard, white, low-volume 384-well and 1536-well microplates using a fluorometric plate reader for detection. The premise of this absorbance assay is based on the fluorescent properties of white microplates and the ability of a colored product to quench the fluorescence signal from the plate by absorbing either the excitation light or the emission light. This method was applied to the detection of inorganic phosphate using Quinaldine red and Malachite green dyes and to the monitoring of alkaline phosphatase hydrolysis of p-nitrophenyl phosphate. These assays can be carried out in low volumes, give robust screening statistics, and can be accomplished with a simple, inexpensive fluorometric plate reader.     

An approach to understand the complexation of supramolecular dye Congo red with immunoglobulin L chain lambda

Congo red, a dye of high self-assembling tendency, has been found to form complexes with proteins by adhesion of the ribbon-like supramolecular ligand to polypeptide chains of beta-conformation. Complexation is allowed by local or global protein instability, facilitating penetration of the dye to the locus of its binding. At elevated temperatures, L chain lambda of myeloma origin was found to form two distinct complexes with Congo red, easily differentiated in electrophoresis as slow- and fast-migrating fractions, bearing four- and eight-dye-molecule ligands, respectively, in the V domain of each individual chain. The slow-migrating complex is formed after displacement of the N-terminal polypeptide chain fragment (about 20 residues) from its packing locus, thereby exposing the entrance to the binding cavity. In this work the formation and stability of this complex was studied by molecular dynamics (MD) simulations. The effect of three- and five-molecule ligands introduced to the site binding the dye was also analyzed in an attempt to understand the formation of fast-migrating complexes. The wedging of the ligand containing five dye molecules, hence longer than established experimentally as the maximum for the slow-migrating complex, was found to generate significant structural changes. These changes were assumed to represent the crossing of the threshold on the way to forming a fast-migrating complex more capacious for dyes. They led to almost general destabilization of the V domain, making it susceptible to extra dye complexation. Theoretical studies were designed in close reference to experimental findings concerning the number of dye molecules in the ligand inserted to the site binding the dye, the location of the site in the domain, and the conditions of formation of the complexes. The results of the two kinds of studies appeared coherent.     

Candidate Inhibitor of the Volume-Sensitive Kinase Regulating K-Cl Cotransport: The Myosin Light Chain Kinase Inhibitor ML-7

K-Cl cotransport, KCC, is activated by swelling in many cells types, and promotes volume regulation by a KCl efflux osmotically coupled to water efflux. KCC is probably activated by swelling-inhibition of a kinase, permitting dephosphorylation, and activation of the cotransporter by a phosphatase. The myosin light chain kinase (MLCK) inhibitor ML-7 inhibits transporters activated by shrinkage. In red blood cells from three mammalian species, ML-7 stimulated KCC in a volume-dependent manner. Relative stimulation was greatest in more shrunken cells. Stimulation was reduced by moderate cell swelling and abolished by further swelling. The half-maximal stimulation is at ∼20 μm ML-7, 50-fold greater than the IC₅₀ for inhibition of MLCK in vitro. Stimulation of KCC by ML-7 did not require cell Ca, while MLCK does. Therefore the target of ML-7 in stimulating KCC in red cells is probably not MLCK. The evidence favors stimulation of KCC by ML-7 by inhibiting the volume-sensitive kinase. Qualitatively similar effects of ML-7 on KCC in red cells from three mammalian species suggest a general mechanism. Received: 17 March 2000/Revised: 28 July 2000     

Comparative studies of the protein composition of red blood cell membranes from eight mammalian species

The polypeptide pattern of red blood cell (RBC) membranes from cow, sheep, horse, rabbit, guinea pig, rat, mouse, analyzed by polyacrylamide gel electrophoresis, was compared to human RBC counterpart. Some qualitative and quantitative differences were noted. Among the high molecular weight components the bands 2.1- 2.3 appeared slightly decreased in rabbit and rat and increased in sheep RBC membranes. Band 3 appeared to have a higher molecular weight in the cow, guinea pig and mouse RBCs, and a lower molecular weight in the sheep RBCs. Band 4.1 from the RBC membranes of cow, sheep, rabbit and guinea pig was splitted into two sub-bands, while band 4.2 overlapped with band 4.1 in horse and guinea pig RBC membranes. There are marked differences in the number and position of bands in the 4.5 region, while band 4.9 is present in higher amounts in horse, rabbit and guinea pig RBC membranes. Band 6 (glyceraldehyde 3-phosphate dehydrogenase) was undetectable in horse, rat and mouse RBC membranes and was decreased in sheep, rabbit and guinea pig. There are also major differences in the region of band 7 and below ("post-7"). Band 8 was undetectable in horse, cow and guinea pig, and was in higher amounts in rat. A band corresponding to a molecular weight of about 22 kD in the "post-8" region was present only in guinea pig RBC membranes.     

Red Chlorophylls in the Exciton Model of Photosystem I

Structural arrangement of pigment molecules of Photosystem I of photosynthetic cyanobacterium Synechococcus elongatus is used for theoretical modeling of the excitation energy spectrum. It is demonstrated that a straightforward application of the exciton theory with the assumption of the same molecular transition energy does not describe the red side of the absorption spectrum. Since the inhomogeneity in the molecular transition energies caused by a dispersive interaction with the molecular surrounding cannot be identified directly from the structural model, the evolutionary search procedure is used for fitting the low temperature absorption and circular dichroism spectra. As a result, one dimer, three trimers and one tetramer of chlorophyll molecules responsible for the red side of the absorption spectrum with their assignment to the spectroscopically established three bands at 708, 714 and 719 nm are determined. All of them are found to be situated not in the very close vicinity of the reaction center but are encircling it almost at the same distance. In order to explain the unusual broadening on the red side of the spectrum the exciton state mixing with the charge transfer (CT) states is considered. It is shown that two effects can be distinguished as caused by mixing of those states: (i) the oscillator strength borrowing by the CT state from the exciton transition and (ii) the borrowing of the high density of the CT state by the exciton state. The intermolecular vibrations between two counter-charged molecules determine the high density in the CT state. From the broad red absorption wing it is concluded that the CT state should be the lowest state in the complexes under consideration. Such mixing effect enables resolving the diversity in the molecular transition energies as determined by different theoretical approaches.     

Simultaneous infection by red rot and chytrid diseases in <Emphasis Type="Italic">Porphyra yezoensis</Emphasis>Ueda

This paper presents the results of a study on the diseases of Porphyra yezoensisUeda along the north coast of China, where red rot (Pythium porphyrae) and the chytrid Olpidiopsis sp. diseases were both found to be present. Infection by the mycelia of Pythium porphyraeand the thallus of Olpidiopsis sp. was studied in detail. At the early stage of infecton the mycelia of Pythium porphyraeand the fungus of chytrid can be found in host cells at the same time. In the middle and late stages of the complication, it mainly appears as red rot disease, toward the end appearing almost completely as red rot disease. The complication even can be found on the cells of fronds from the freeze-storage nori nets. However, the freeze-storage nets can help prevent spread of the infection and improve nori quality.     

Base cation stimulation of mycorrhization and photosynthesis of sugar maple on acid soils are coupled by foliar nutrient dynamics

The nutritional benefits that mycorrhizal associations provide to plants may be constrained by acidic soil conditions resulting in decreased photosynthetic function. Sugar maple (Acer saccharum) and red maple (Acer rubrum) seedlings were grown on a native acidic (pH 4.1) soil both unamended and amended with base cations (pH 6.2). In a second study a fungicide treatment was included. Foliar nutrition, mycorrhizal colonization, photosynthesis and their relationships were assessed. On the native soil, red maple maintained higher levels of mycorrhizal colonization and photosynthesis than sugar maple but showed little response to base cation amendments. Mycorrhizal colonization and photosynthesis of sugar maple increased significantly in response to base cation amendments. Correlations were observed among mycorrhizal colonization, foliar nutrition and photosynthesis. The fungicide treatment indicated that 50% of the base cation-induced increase in sugar maple photosynthesis was mycorrhiza related. The results suggest that base cation stimulation of mycorrhization and photosynthesis of sugar maple on acid soils are coupled by foliar nutrient dynamics. Red maple exhibits much less sensitivity to these same edaphic conditions.