Crystallization and preliminary x-ray diffraction studies of two new antigen-antibody (lysozyme-Fab) complexes

The complexes between the Fab fragments of two monoclonal anti-lysozyme antibodies, Fab10.6.6 (high affinity) and D44.2 (lower affinity), and their specific antigen, hen egg-white lysozyme, have been crystallized. The antibodies recognize an antigenic determinant including Arg68, but differ significantly in their association constants for the antigen. Two crystalline forms were obtained for the complex with FabF10.6.6, the higher affinity antibody. One of them is monoclinic, space group P21, with unit cell dimensions a = 145.6 A, b = 78.1 A, c = 63.1 A, beta = 89.05 degrees, consistent with the presence of two molecules of the complex in the asymmetric unit. These crystals diffract X-rays beyond 3 A making this form suitable for high-resolution X-ray diffraction studies. The second form crystallizes in the triclinic space group P1, with unit cell dimensions a = 134.0 A, b = 144.7 A, c = 98.6 A, alpha = 90.30 degrees, beta = 97.1 degrees, gamma = 90.20 degrees, consistent with the presence of 10 to 12 molecules of the complex in the unit cell. These crystals do not diffract X-rays beyond 5 A resolution. The antigen-antibody complex between FabD44.2, the lower affinity antibody, and hen egg-white lysozyme crystallizes in space group P2(1)2(1)2(1), with unit cell dimensions a = 99.7 A, b = 167.3 A, c = 84.7 A, consistent with the presence of two molecules of the complex in the asymmetric unit. These crystals diffract X-rays beyond 2.5 A resolution.     

Trapping of γ-Decalactone by Adsorption on Hydrophobic Sorbents : Application to the bioconversion of methyl ricinoleate by the yeast Sporidiobolus salmonicolor

Trapping by adsorption on hydrophobic porous polymers was used to selectively remove -decalactone from the complex bioconversion medium. Several sorbents were tested : activated carbon, and three porous polystyrene-type polymers (Porapak Q, Chromosorb 105, and Resin SM4). The sorption isotherms were determined in water and in a model bioconversion medium without microorganisms. In the last part of the study, the application to the production of -decalactone by Sporidiobolus salmonicolor was carried out. Hydrophobic porous adsorbents are compatible with the bioconversion and protect the yeast from the toxic effect of -decalactone.     

Predicting community characteristics from habitat conditions: fluvial fish and hydraulics

1. One current approach to the prediction of community characteristics is to use models of key local-scale processes (e.g. niche dimensions) affecting individuals and to estimate the effects of these attributes over larger scales. We tested this approach, focusing on how the hydraulic habitat structures fluvial fish communities. 2. We used a recent statistical habitat model to predict fish community characteristics in eleven reaches in the Rhône river basin in France. Predictions were made ‘blindly’ since most reaches were not used to calibrate the model. The model reflects species preferences for local hydraulics. We made predictions of the fish community from the local hydraulic conditions found in the reaches under low flow conditions. The overall abundance and the relative abundance (both as indices) of fish species, specific size classes and species traits (i.e. reproductive, trophic, morphological and others) were predicted. We summarized our predictions of the relative abundance of species as two ‘community structure indices’ using Principal Component Analysis. 3. Our predictions from low-flow hydraulics were compared with long-term observations of fish communities. The relative abundance of species actually observed depended largely on zoogeographic factors within the Rhône basin which could not be predicted by the model. The model predicted 13% of the variance in the indices of relative abundance at the species level and 23% of this variance at the trait level for all zoogeographic regions combined. However, when focused on reaches within a geographic region, the model explained up to 47% of the same variance. Therefore, geographic regions act as ‘filters’ on the relative abundance of species, but hydraulics do affect fish communities within a given geographical context. 4. For the synthetic ‘community structure indices’, we obtained good predictions from hydraulics independently of the geographical context (variance explained up to 95%). These indices were linked to simple key hydraulic characteristics of river reaches (Froude and/or Reynolds number). The indices enabled interpretations of the links between hydraulics, geomorphology, discharge and community patterns. These links were consistent with existing knowledge of species and their traits. 5. In addition to the above validations, the habitat model partly explained the observed effects of impoundment on fish communities. 6. The present results show that stream hydraulics strongly impact fish community structure. Consequently, our findings confirm that community characteristics can be predicted using models of the local-scale habitat requirements of the species forming the community.     

Crystallization,preliminary X-ray diffraction study,and crystal packing of a complex between anti-Hen lysozyme antibody F9.13.7 and Guinea-fowl lysozyme

The complex formed between the Fab fragment of a murine monoclonal anti-hen egg lysozyme antibody F9.13.7 and the het-erologous antigen Guinea-fowl egg lysozyme has been crystallized by the hanging drop technique. The crystals, which diffract X-rays to 3 Å resolution, belong to the monoclinic space group P2₁, with a = 83.7 Å, b = 195.5 Å, c = 50.2 Å, β = 108.5° and have two molecules of the complex in the asymmetric unit The three-dimensional structure has been determined from a preliminary data set to 4 Å using molecular replacement techniques. The lysozyme–Fab complexes are arranged with their long molecular axes approximately parallel to the crystallo-graphic unique axis. Fab F9.13.7 binds an anti-genie determinant that partially overlaps the epitope recognized by antilysozyme antibody HyHEL10. © 1993 Wiley-Liss, Inc.     

Characterization of two crystal forms of Clostridium thermocellum endoglucanase CelC

Endoglucanase CelC from Clostridium thermocellum expressed in Escherichia coli has been crystallized in two different crystal forms by the hanging drop method. Crystals of form I were grown with polyethylene glycol as a precipitant. They are orthorhombic, space group P2₁2₁2₁, with cell dimensions a =51.4 Å, b =84.3 Å, and c =87.5 Å. Crystals of form II, obtained in ammonium sulfate solutions, belong to the tetragonal space group P4₁2₁2 (or P4₃2₁2) with cell dimensions of a = b = 130.7 Å and c = 69.6 Å. Diffraction data to 2.8 Å resolution were observed for both crystal forms with a rotating anode generator. Preliminary oscillation images of the orthorhombic form I crystals using a synchrotron radiation source show diffraction to 2.2 Å resolution, indicating that these crystals are suitable for high resolution crystallographic analysis. © 1994 Wiley-Liss, Inc.     

Fish habitat preferences in large streams of southern France

1. Relationships between fish and their habitat over whole geographic regions, which are evident from studies of many streams and species, can improve understanding of lotic communities and provide reliable management tools. Nevertheless, most habitat preference studies have been based on single sites, and confined to small streams and to game species.
2. Regional habitat preference models, based on local velocity, depth and roughness, were developed for twenty-four species and their size classes commonly found in large European streams. Fish surveys were conducted in six large streams in southern France over an 8-year period. To limit the influences of habitat variables other than those studied, we estimated fish preferences within each survey and averaged this information across surveys. Preferences were fitted with confidence intervals and their sensitivity to field uncertainty was evaluated.
3. Most species and size classes had significant preferences for local habitat conditions which were consistent across the region. Habitat preferences predominant in the region overall were not always observed at any one site, but habitat conditions preferred on average in the region were never actually avoided locally. These results support the use of regional preference models for fish and the development of similar models for other lotic groups whose sensitivity to local habitat conditions has been reported elsewhere.     

High resolution land cover data improve understanding of mechanistic linkages with stream integrity

相似文献   

Mechanistic mathematical model for in vivo aroma release during eating of semiliquid foods

The paper describes a mechanistic mathematical model for aroma release in the oropharynx to the nasal cavity during food consumption. The model is based on the physiology of the swallowing process and is validated with atmospheric pressure chemical ionization coupled with mass spectrometry measurements of aroma concentration in the nasal cavity of subjects eating flavored yogurt. The study is conducted on 3 aroma compounds representative for strawberry flavor (ethyl acetate, ethyl butanoate, and ethyl hexanoate) and 3 panelists. The model provides reasonably accurate time predictions of the relative aroma concentration in the nasal cavity and is able to simulate successive swallowing events as well as imperfect velopharyngeal closure. The most influent parameters are found to be the amount of the residual product in the pharynx and its contact area with the air flux, the volume of the nasal cavity, the equilibrium air/product partition coefficient of the volatile compound, the breath airflow rate, as well as the mass transfer coefficient of the aroma compound in the product, and the amount of product in the mouth. This work constitutes a first step toward computer-aided product formulation by allowing calculation of retronasal aroma intensity as a function of transfer and volatility properties of aroma compounds in food matrices and anatomophysiological characteristics of consumers.     

A lubrication analysis of pharyngeal peristalsis: Application to flavour release

After eating a liquid or a semi-liquid food product, a thin film responsible for the dynamic profile of aroma release coats the pharyngeal mucosa. The aim of this article was to analyse the fluid mechanics of pharyngeal peristalsis and to develop a simple biomechanical model in order to understand the role of saliva and food bolus viscosity on the coating of pharyngeal mucosa. We began by analysing the physiology and the biomechanics of swallowing in order to determine relevant model assumptions. This analysis of the literature clarified the types of mechanical solicitations applied on the food bolus. Moreover, we showed that the pharyngeal peristalsis in the most occluded region is equivalent to a forward roll coating process, the originality of which is lubrication by a film of saliva. A model based on the lubrication theory for Newtonian liquids was developed in dimensionless form. The parametric study showed the strong influence of relative saliva thickness on the food bolus coating. A specific experimental device was designed that confirms the model predictions. Two sets of conditions that depend on the relative thickness of saliva were distinguished. The first is characterised by a relatively thin film of saliva: food bolus viscosity has a strong impact on mucosa coating. These phenomena are well represented by the model developed here. The second is obtained when the saliva film is relatively thick: hydrodynamic mixing with saliva, interdiffusion or instabilities may govern mucosa coating. Finally, these results were extrapolated to determine the influence of food bolus viscosity on the dynamic profile of flavour release according to physiological parameters.