Persistent Effects of Short-term, High Exposure to Chlorine Gas on Physiology and Growth of Pinus ponderosa andPseudotsuga menziesii

Following a single acute exposure to chlorine gas, persistenteffects on epicuticular waxes, cuticular transpiration, treegrowth and mortality were studied in foliage of Pinus ponderosaand Pseudotsuga menziesii for three growing seasons. Chlorinegas exposure caused foliar injury to both exposed foliage andfoliage that flushed after exposure (P < 0.05). The tendencyto form films of water rather than droplets was greater in directlyexposed foliage (P < 0.001). Rates of cuticular transpirationwere higher for directly and indirectly exposed foliage of Pinusponderosa up to 1 year after exposure and up to 6 months afterexposure for directly exposed Pseudotsuga menziesii(P < 0.001),after which P. menziesii needles defoliated. Total water content(TWC) and relative water content were significantly correlatedwith foliar injury (P < 0.05). TWC was lower for directlyexposed foliage up to 1 year after exposure (P < 0.001).There was no persistent negative effect on F_v/F_m ratios after1 year. Exposure to chlorine gas did not affect needle lengthor annual shoot increment growth, but exposure was correlatedwith increased bud production. Needle longevity of foliage thatflushed 2 months after exposure was reduced significantly (P< 0.001). Annual stem increment growth for both species decreasedover at least three growing seasons following chlorine gas exposure(P < 0.001), and depended on distance from the spill site.Cone production was lower for exposed Pinus ponderosa treescompared to controls (P < 0.05), and tree mortality was higherwithin approx. 50 m of the release site forPseudotsuga menziesii. Growth responses for both conifers agreed well with predictedpatterns of carbon allocation after defoliation caused by chlorinegas exposure. Copyright 2001 Annals of Botany Company Pinus ponderosa, Pseudotsuga menziesii, conifers, chlorine gas, leaf wettability, cuticular transpiration, water relations, growth, mortality     

Calcium-induced changes in permeability of dioleoylphosphatidylcholine model membranes containing bovine heart cardiolipin

At calcium concentrations up to about 4 mM a selective permeability increase of cardiolipin/dioleoylphosphatidylcholine (50:50, mol%) membranes for calcium and its chelator arsenazo III is observed. Under these conditions calcium does not occupy all the binding sites of cardiolipin at the membrane interface and no vesicle-vesicle interactions are found. Lowering of the cardiolipin content of the vesicles to 20 mol% extends the calcium concentration range in which a selective permeability for calcium and arsenazo III is appearing up to about 12 mM. We suggest that the observed selective permeability increase is caused by transient formation of inverted micellar structures in the membrane with cardiolipin as translocating membrane component for calcium and arsenazo III. At calcium concentrations of 4 mM and higher for 50 mol% cardiolipin-containing vesicles a general permeability increase is found together with calcium-cardiolipin binding in a 1:1 stoichiometry, vesicles aggregation and, above 8 mM of calcium, vesicle fusion. The loss of barrier function of the membrane under these conditions is correlated with vesicle aggregation and may be explained by a transition from a bilayer into a hexagonal HII organization of the phospholipids.     

Analysis of the active site of the flavoprotein p-hydroxybenzoate hydroxylase and some ideas with respect to its reaction mechanism

The flavoprotein p-hydroxybenzoate hydroxylase has been studied extensively by biochemical techniques by others and in our laboratory by X-ray crystallography. As a result of the latter investigations, well-refined crystal structures are known of the enzyme complexed (i) with its substrate p-hydroxybenzoate and (ii) with its reaction product 3,4-dihydroxybenzoate and (iii) the enzyme with reduced FAD. Knowledge of these structures and the availability of the three-dimensional structure of a model compound for the reactive flavin 4a-hydroperoxide intermediate has allowed a detailed analysis of the reaction with oxygen. In the model of this reaction intermediate, fitted to the active site of p-hydroxybenzoate hydroxylase, all possible positions of the distal oxygen were surveyed by rotating this oxygen about the single bond between the C4a and the proximal oxygen. It was found that the distal oxygen is free to sweep an arc of about 180 degrees in the active site. The flavin 4a-peroxide anion, which is formed after reaction of molecular oxygen with reduced FAD, might accept a proton from an active-site water molecule or from the hydroxyl group of the substrate. The position of the oxygen to be transferred with respect to the substrate appears to be almost ideal for nucleophilic attack of the substrate onto this oxygen. The oxygen is situated above the 3-position of the substrate where the substitution takes place, at an angle of about 60 degrees with the aromatic plane, allowing strong interactions with the pi electrons of the substrate. Polarization of the peroxide oxygen-oxygen bond by the enzyme may enhance the reactivity of flavin 4a-peroxide.     

Preference for linking element -en- in Dutch noun-noun compounds: native speakers and second language learners of Dutch

In Dutch, variation occurs in the formation of noun-noun compound words. Some compounds always add the linking element -en- between the two nouns; some compounds never use such a linking element; and still others allow both options. The element -en- is homophonous with the regular plural ending in Dutch, and we therefore investigated if plural semantics creates a preference for the linking element -en- in novel Dutch noun-noun compounds. We also investigated if the preference for linking -en- is influenced by just meaning (i.e., a semantic plural), form (i.e., a formal plural), or perhaps both. The influence of native language on preferences for Dutch compounds was also investigated. In study 1, we tested native speakers of Dutch; in study 2, Frisian-Dutch bilinguals; and, in study 3, speakers of German with Dutch as a second language. Plurality played a role in the preferences for Dutch compound formation in all tested groups. For native speakers of Dutch, Frisian, and German, moreover, the preference for a linking element in novel Dutch compounds was influenced by both the semantic plural and the formal plural. However, these effects were smaller for the native speakers of German. These findings confirm the findings of earlier studies (e.g. Schreuder et al. in Language and Cognitive Processes 13(5):551–573, 1998) showing linking -en- to carry an intrinsic plural meaning. Kiparsky’s level-ordering hypothesis (Linguistics in the morning calm, pp. 3–91, 1982) and Pinker’s words-and-rules theory (Words and rules: the ingredients of language, 1999) are re-considered in light of the present findings.     

Modelled influences of non-exchanging trichomes on leaf boundary layers and gas exchange

The two main resistances in the exchange of gases between plants and the atmosphere are stomatal and boundary layer resistances. We modeled boundary layer dynamics over glabrous and pubescent leaves (assuming non-exchanging trichomes) with leaf lengths varying from 0.01 to 0.2 m, and windspeeds of 0.1-5.0 m x s(-1). Results from theoretical and semi-empirical formulae were compared. As expected, boundary layer thickness decreased with decreasing leaf length and increasing windspeed. The presence of trichomes increased leaf surface roughness, resulting in lowered Reynolds numbers at which the boundary layer became turbulent. This effect is especially important at low windspeeds and over small leaves, where the Reynolds number over glabrous surfaces would be low. We derived a new simple dimensionless number, the trip factor, to distinguish field conditions that would lead to a turbulent boundary layer based on the influence of trichomes. Because modeled rates of CO2 and H2O(v) exchange over turbulent boundary layers are one or more orders of magnitude faster than over laminar boundary layers, a turbulent boundary layer may lead to increased carbon uptake by plants. The biological trade-off is potentially increased transpirational water loss. However, in understory habitats characterized by low windspeeds, even a few trichomes may increase turbulence in the boundary layer, thus facilitating photosynthetic gas exchange. Preliminary field data show that critical trip factors are exceeded for several plant species, both in understory and open habitats.     

Novel factor Xa inhibitors based on a benzoic acid scaffold and incorporating a neutral P1 ligand

A series of novel, highly potent, achiral factor Xa inhibitors based on a benzoic acid scaffold and containing a chlorophenethyl moiety directed towards the protease S1 pocket is described. A number of structural features, such as the requirements of the P1, P4 and ester-binding pocket ligands were explored with respect to inhibition of factor Xa. Compound 46 was found to be the most potent compound in a series of antithrombotic secondary assays.     

Factor Xa inhibitors based on a 2-carboxyindole scaffold: SAR of neutral P1 substituents

A series of novel, highly potent 2-carboxyindole-based factor Xa inhibitors is described. Structural requirements for neutral ligands, which bind in the S1 pocket of factor Xa were investigated with the 2-carboxyindole scaffold. This privileged fragment assembly approach yielded a set of equipotent, selective inhibitors with structurally diverse neutral P1 substituents.     

Design,synthesis, and structure-activity relationship of a new class of amidinophenylurea-based factor VIIa inhibitors

Selective inhibition of coagulation factor VIIa has recently gained attraction as interesting approach towards antithrombotic treatment. Using parallel synthesis supported by structure-based design and X-ray crystallography, we were able to identify a novel series of amidinophenylurea derivatives with remarkable affinity for factor VIIa. The most potent compound displays a K(i) value of 23 nM for factor VIIa.     

Application of conformationally restricted peptidomimetics to modeling the bound conformation of peptide antagonists with the IL-1 receptor

A collection of complementary peptide caricatures that closely mimic low-energy (presumably highly populated) conformations of amino acids of interest would constitute a valuable tool set to study the interactions of small peptide ligands with their biological targets. Our general strategy for the design, synthesis and application of peptidomimetics is presented. An illustration of how structural information from mimetics combined with cutting edge biophysical data can be used to derive a model for the bound conformation of an 11-mer peptide antagonist with the IL-1 receptor is given.