Short communication: Effect of water activity on cell growth and phenol oxidase production by Streptomyces cyaneus var. viridochromogenes in surface culture

In surface cultures of Streptomyces cyaneus var. viridochromogenes, NaCl depressed water activity (a _w) without supporting growth. Reducing a _w from 0.987 to 0.951 led to 3- and 4-fold increases in intracellular and extracellular phenol oxidase activities, respectively.     

冬小麦根表面氧化还原活力的研究

证实了两个不同品种的冬小麦根系表面存在着氧化ＮＡＤＨ和还原Ｋ３Ｆｅ（ＣＮ）６的氧化的活力。还原铁氰化物活力在ＰＨ５．５到８．５范围内随着ＰＨ值升高而增大,温度在１５℃到４５℃范围内随温度升高还原活力增强,４５℃达最高值,５５℃时活力急剧下降。     

人体超微弱发光图像中的信号检验

用近期研制的具有单光子探测能力的超高灵敏度成像系统获得了人体体表生物超微弱发光的强度数据。为分析图像中的信号检验,二项分布被用于人手不同时间累积发光图像中的信号显著性检验,证实人手存在超微弱生物发光,手指的发光强度在３００～５５０ｐｈｏｔｏｎｓ／ｓ范围内,全手的发光强度在８５０～１２００ｐｈｏｔｏｎｓ／ｓ范围内。     

Leaf surface properties of Norway spruce needles exposed to sulphur dioxide and ozone in an open-air fumigation system at Liphook

Samples of current-year and 1-year-old foliage were taken from Norway spruce (Picea abies (L.) Karst.) trees in April 1991, 4 months after a 3–4 year controlled fumigation with O₃ and SO₂ in the open at Liphook, south-east England. Trees were grown in seven plots, and treated in a factorial design with three levels of SO₂ and two levels of O₃ (ambient and c. 1.3 × ambient), with an extra ambient air plot. All statistical analyses were made on plot means. Leaf wettability, as measured by the contact angle of water droplets, was significantly affected by needle age and by SO₂ treatment (P≤0–05. in older needles, decreasing with increasing SO₂ concentration. There was no effect of O₃ on wettability, and no effect of any treatment on amounts of surface wax extracted by immersion of needles in chloroform. Electrolyte leakage rates from detached current-year needles were not affected by prior exposure to O₃, but decreased significantly (P= 0.034) with increasing exposure to SO₂. There was no detectable effect of fumigation on the rate of water loss from detached needles. Similarly, there was no effect of fumigation on the dry weight/fresh weight ratio of needles. The total sulphur content of needles increased significantly (P≤0.0001) with exposure to SO₂ and with needle age. Amounts of water-extractable sulphate, however, varied greatly among plots, but with no pattern with respect to fumigation treatment. It is concluded that leaf wettability and electrolyte leakage rates may be good indicators of the persistent effects of SO₂ on Norway spruce growing in the open air, and that the observed changes in leaf surface properties in response to SO₂ fumigation have implications for the processes, both biotic and abiotic, that occur on leaf surfaces.     

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.     

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.