Abundance of phytoseiid mites on Vitis species: effects of leaf hairs,domatia, prey abundance and plant phylogeny

We observed the number of predatory mites (Phytoseiidae:Typhlodromus caudiglans) on the foliage of 20 North American species of grapes (Vitis spp) plus the domesticated EuropeanVitis vinifera, all grown in a common garden. We found relatively few phytophagous mites. The numbers of phytophagous mites were not correlated with the plant characteristics that we measured. We found approximately five times as many predatory mites as phytophagous mites and the numbers of these phytoseiid predators were not affected by the availability of prey. Similarly, numbers of phytoseiids were unaffected by plant gender and, hence, the availability of pollen, another source of food. The numbers of phytoseiids were not clustered according to the taxonomic grouping of the tested plant species. Leaf surface characteristics explained over 25% of the variance in the numbers of phytoseiids. Numbers of phytoseiids were positively associated with the density of vein hairs, the density of bristles in leaf axils, and the presence of leaf domatia. These results suggest that sheltered habitats rather than food availability may limit the numbers of phytoseiid mites on grapevines.     

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Stimulates Adenylyl Cyclase and Phospholipase C Activity in Rat Cerebellar Neuroblasts

Abstract: The presence of receptors for the novel neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) has been recently demonstrated in the external granule cell layer of the cerebellum, a germinative matrix that generates the majority of cerebellar interneurons. In the present study, we have taken advantage of the possibility of obtaining a culture preparation that is greatly enriched in immature cerebellar granule cells to investigate the effect of PACAP on the adenylyl cyclase and phospholipase C transduction pathways. The two molecular forms of PACAP, i.e., 27-(PACAP27) and 38-(PACAP38) amino-acid forms of PACAP, induced a dose-dependent stimulation of cyclic AMP production in granule cells. The potencies of PACAP27 and PACAP38 were similar (ED₅₀ = 0.12 ± 0.01 and 0.23 ± 0.07 n M , respectively), whereas vasoactive intestinal polypeptide (VIP) was ∼100 times less potent. PACAP27 and PACAP38 also induced a dose-dependent stimulation of polyphosphoinositide breakdown (ED₅₀ = 19.1 ± 6.3 and 13.4 ± 6.0 n M , respectively), whereas VIP had no effect on polyphosphoinositide metabolism. The effect of PACAP38 on inositol phosphate formation was significantly reduced by U-73122 and by pertussis toxin, indicating that activation of PACAP receptors causes stimulation of a phospholipase C through a pertussis toxin-sensitive G protein. In contrast, forskolin and dibutyryl cyclic AMP did not affect PACAP-induced stimulation of inositol phosphates. Taken together, the present results demonstrate that PACAP stimulates independently the adenylyl cyclase and the phospholipase C transduction pathways in immature cerebellar granule cells. These data favor the concept that PACAP may play important roles in the control of proliferation and/or differentiation of cerebellar neuroblasts.     

Mutant Escherichia coli penicillin acylase with enhanced stability at alkaline pH

Increased stability at alkaline pH should be a valuable attribute for the utilization of penicillin acylase in bioreactors employed to convert penicillins into 6-aminopenicillanic acid, a precursor of semisynthetic penicillins. In these systems, base is added for pH control, which results in local alkaline conditions that promote enzyme inactivation. Hydrolysis and synthesis reactions are also pH dependent. Here, we report work in which the gene coding for Escherichia coli penicillin acylase was subjected to oligonucleotide-directed random mutagenesis at regions coding for amino acids predicted to be at the surface of the enzyme. The resulting mutant library, cloned in E. coli, was screened by a filter paper assay of the colonies for the presence of penicillin acylase activity with enhanced stability at alkaline pH. Characterization of one of the selected clones revealed the presence of a mutation, Trp431-Arg, which would presumably alter the surface charge of the protein. In vitro experiments demonstrated a near twofold increase in the half-life of the mutant enzyme when stored at pH 8.5 as compared with the wild-type enzyme, with a comparable specific activity at several pH values. In general, the mutant displayed increased stability toward the basic side in the pH-stability profile. (c) 1995 John Wiley & Sons, Inc.     

Theoretical Study of the TiO2 and MgO Surface Acidity and the Adsorption of Acids and Bases

We present ab-initio periodic Hartree–Fock calculations (crystal program) of small molecules on TiO₂ and MgO. The adsorption of the molecules may be molecular or dissociative. This depends on their acid and basic properties in the gas phase. For the molecular adsorption, the molecules are adsorbed as bases on Ti(+IV) sites, the adsorption energies correlate with the proton affinities. The dissociations on the surface correlate with the gas phase cleavages: thus, the dissociation of MeOH leads to a preferential basic cleavage (the fragment HO– is adsorbed on a Ti⁺⁴ ion and the fragment Me⁺ is adsorbed on a O²– ion of the oxide). The opposite result is obtained with MeSH. Another important factor is the adsorbate–adsorbate interaction: favorable cases are a sequence of H-bonds for the hydroxyl groups resulting from the water dissociation and the mode of adsorption for the ammonium ions. Lateral interactions also force the adsorbed CO₂ molecules to bend over the surface so that their mutual orientation resembles the geometry of the CO₂ dimer. With respect to water adsorption, MgO appears to be a basic oxide. As experimentally observed, NH₃ adsorbs preferentially on TiO₂ and CO₂ on MgO. However, this difference of reactivity should not be expressed in terms of acid vs. basic behaviour but in terms of hard and soft acidity. The MgO surface is a 'soft' acidic surface that reacts preferentially with the soft base, CO₂.     

Surface water chemistry characteristics in the Lake Storgrønningen drainage area, Høylandet, during periods of high and low discharge

The surface water chemistry of Høylandet has beenstudied by performing two synoptic surveys, duringhigh runoff in the autumn of 1986 and during a lowflow period in the summer of 1988. Based on watersamples of up to 38 chemical variables from 75 sites,analyses show considerable variation in the chemicalcomposition. There is a strong altitude gradient, i.e.very dilute poorly buffered waters dominate at higherelevations near the timberline while progressivelyhigher salt content and alkalinities arecharacteristic at lower altitudes more dominated byforests. The influence of mires is less pronounced.The overall water quality is of oligotrophic naturewith low concentrations of strong acid anions andmetals known to be enriched under acidifiedconditions. The natural pH gradients are considerablebut with no indication of anthropogenic acidification.The data provide little support for the hypothesisthat in-catchment production of organically derivedacidity leads to acid runoff, which in thesecatchments appears compensated by increasedweathering. The findings are in general accordancewith other Høylandet catchment studies. It isconcluded that this area may serve as a representativepristine surface runoff analogue for catchmentscurrently affected by atmospheric deposition of strongmineral acids.     

Domain Evolution in the α-Amylase Family

The available amino acid sequences of the α-amylase family (glycosyl hydrolase family 13) were searched to identify their domain B, a distinct domain that protrudes from the regular catalytic (β/α)₈-barrel between the strand β3 and the helix α3. The isolated domain B sequences were inspected visually and also analyzed by Hydrophobic Cluster Analysis (HCA) to find common features. Sequence analyses and inspection of the few available three-dimensional structures suggest that the secondary structure of domain B varies with the enzyme specificity. Domain B in these different forms, however, may still have evolved from a common ancestor. The largest number of different specificities was found in the group with structural similarity to domain B from Bacillus cereus oligo-1,6-glucosidase that contains an α-helix succeeded by a three-stranded antiparallel β-sheet. These enzymes are α-glucosidase, cyclomaltodextrinase, dextran glucosidase, trehalose-6-phosphate hydrolase, neopullulanase, and a few α-amylases. Domain B of this type was observed also in some mammalian proteins involved in the transport of amino acids. These proteins show remarkable similarity with (β/α)₈-barrel elements throughout the entire sequence of enzymes from the oligo-1,6-glucosidase group. The transport proteins, in turn, resemble the animal 4F2 heavy-chain cell surface antigens, for which the sequences either lack domain B or contain only parts thereof. The similarities are compiled to indicate a possible route of domain evolution in the α-amylase family. Received: 4 December 1996 / Accepted: 13 March 1997     

Atomic and residue hydrophilicity in the context of folded protein structures

Water-protein interactions drive protein folding, stabilize the folded structure, and influence molecular recognition and catalysis. We analyzed the closest protein contacts of 10,837 water molecules in crystallographic structures to define a specific hydrophilicity scale reflecting specific rather than bulk solvent interactions. The tendencies of different atom and residue types to be the nearest protein neighbors of bound water molecules correlated with other hydrophobicity scales, verified the relevance of crystallographically determined water positions, and provided a direct experimental measure of water affinity in the context of the folded protein. This specific hydrophilicity was highly correlated with hydrogen-bonding capacity, and correlated better with experimental than computationally derived measures of partitioning between aqueous and organic phases. Atoms with related chemistry clustered with respect to the number of bound water molecules. Neutral and negatively charged oxygen atoms were the most hydrophilic, followed by positively-charged then neutral nitrogen atoms, followed by carbon and sulfur atoms. Agreement between observed side-chain specific hydrophilicity values and values derived from the atomic hydrophilicity scale showed that hydrophilicity values can be synthesized for different functional groups, such as unusual side or main chains, discontinuous epitopes, and drug molecules. Two methods of atomic hydrophilicity analysis provided a measure of complementarity in the interfaces of trypsin:pancreatic trypsin inhibitor and HIV protease:U-75875 inhibitor complexes. © 1995 Wiley-Liss, Inc.     

Removal of toluene in waste gases using a biological trickling filter

The removal of toluene from waste gas was studied in a trickling biofilter. A high level of water recirculation (4.7 m h^–1) was maintained in order to keep the liquid phase concentration constant and to achieve a high degree of wetting. For loads in the range from 6 to 150 g m^–3 h^–1 the maximum volumetric removal rate (elimination capacity) was 35±10 g m^–3 h^–1, corresponding to a zero order removal rate of 0.11±0.03 g m^–2 h^–1 per unit of nominal surface area. The surface removal was zero order above the liquid phase concentrations of approximately 1.0 g m^–3, corresponding to inlet gas concentrations above 0.7–0.8 g m^–3. Below this concentration the surface removal was roughly of first order. The magnitude of the first order surface removal rate constant, k_1A , was estimated to be 0.08–0.27 m h^–1 (k_1A a=24–86 h^–1). Near-equilibrium conditions existed in the gas effluent, so mass transfer from gas to liquid was obviously relatively fast compared to the biological degradation. An analytical model based on a constant liquid phase concentration through the trickling filter column predicts the effluent gas concentration and the liquid phase concentration for a first and a zero order surface removal. The experimental results were in reasonable agreement with a very simple model valid for conditions with an overall removal governed by the biological degradation and independent of the gas/liquid mass transfer. The overall liquid mass transfer coefficient, K_La, was found to be a factor 6 higher in the system with biofilm compared to the system without. The difference may be explained by: 1. Difference in the wetting of the packing material, 2. Mass transfer occurring directly from the gas phase to the biofilm, and 3. Enlarged contact area between the gas phase and the biofilm due to a rough biofilm surface.     

Surface modification of polymers: chemical, biological and surface analytical challenges

Surface modification methods can optimise the biocompatibility or the specificity of biointeraction of a biosensor or medical device. With only the surface modified, the manufacture and implantation protocol remain unchanged. This review article summarises some of the chemical, surface analytical and biological challenges associated with surface modification of biosensors and biomedical devices.     

Surface immobilization and entrapping of enzymes on glutaraldehyde crosslinked gelatin particles

A mild and reproducible method has been developed for the surface-immobilization of enzymes on glutaraldehyde crosslinked gelatin beads. In this method glutaraldehyde is used in a dual capacity, as crosslinking agent and as the enzyme coupling agent. Glucoamylase (exo-α-1,4-d-glucosidase, EC 3.2.1.3), β-d-fructofuranosidase (invertase, EC 3.2.1.26) and β-d-glucoside (cellobiase, β-d-glucoside glucohydrolase, EC 3.2.1.21) have been successfully immobilized by this method, on the surface of the crosslinked gelatin particles. The method can be combined with the existing technology for the production of gelatin-entrapped enzymes. Thus, dual immobilized enzyme conjugates of glucoamylase and invertase have been prepared using this method, by entrapment of one enzyme in, and surface-binding of the other to, the gelatin matrix. The coupling of glucoamylase onto cross-linked gelatin particles by precipitation with poly(hexamethylenebiguanide hydrochloride) was also tested.