Critical receptor

Tachykinins and their Receptors. Table7 Critical receptor amino acid residues for the binding of selective NK NK2, or NK3 receptor antagonists at the respective human TK receptors... 

Computational techniques have allowed investigators to use this extensive amount of biochemical and biophysical information to develop the available structural information, including the inactive structure of rhodopsin (T eller et al., 2001), the GDP-bound Gt heterotrimer (Lambright et al., 1994), and NMR structures of the C-termini of Gat and Gy (Kisselev and Downs, 2003 Kisselev et al., 1998), into molecular models of the receptor-G protein complex (Ciarkowski et al., 2005 Fotiadis et al., 2004 Slusarz and Ciarkowski, 2004). Since the C-terminus of Ga, a critical receptor-binding site, is absent in both structures of G protein heterotrimers (Lambright... 

For ecological receptors, a similar approach may be employed for secondary receptors that could be influenced by a change in the soil environment. For instance, it is possible to model the potential for soil to influence an adjacent surface water body and therefore to screen the soil criteria for impacts on an aquatic receptor. When applied, this leads to intercompartment harmonization of standards, by which soil or sediment standards pose no problems for water bodies and vice versa. In addition, it may be possible to use screening-level models to assess the potential for a bioaccumulable substance to influence a tertiary ecological receptor, usually a top predator or a protected species. In this approach, the reference dose can be borrowed from other sources (e.g., use of an aquatic criterion to determine a critical water concentration). The model is then used only to assess how the soil may influence transfer to the critical receptor. However, it should be noted that this type of procedure cannot be used for guideline development related to primary terrestrial receptors since there are no reliable models to estimate dose-response relationships for these receptors. Therefore, other techniques described in this chapter are recommended for screening against primary receptors. 

The final version of CLEA is likely not to consider all of the above. The land use scenario determines which exposure pathways are relevant, who the critical receptor is, and what their activity patterns are. Guideline values are derived for each land use scenario. The Residential with gardens land use scenario is the most sensitive scenario and the Commercial and industrial scenario the least sensitive because of which pathways are considered. As the guideline values are generic, a reasonable worst case is assumed. They may not therefore be suitable for every site. For instance, the Parks, playing fields and open spaces land use has the same... 

The critical receptor depends on the land use scenario. The exposure and averaging periods vary according to who the critical receptor is, and whether the contaminant is being treated as a carcinogen or a non-carcinogen. 

The critical receptor for lead uptake is the child in its second year of life. It is the amount of lead that is taken up in blood, rather than the total soil concentration that is important. CLEA guideline values are based on predictions of contaminant concentration in soil that will result in a given amount of lead in the blood. The exposure to lead from other sources far exceeds the exposure to soil the guideline value for lead is based on the idea of proportional reduction. This means that if e.g. 10% of the overall exposure to lead comes from soils, only 10% of the reduction required to bring blood lead within acceptable concentrations should be due to the soil. 

This points to allosteric regulation of the critical receptor site common to all malodors. The allosteric site undergoes ligand formation with the AMAL active profile. This process causes changes in the conformation of the regulatory subunit of the detector enzyme which alters the overall geometry of the sterically indifferent critical receptor site to such an extent that its activity for ligand formation with malodors is decreased or totally inhibited. Consequent-... 

Some of the confusion resulting from this diversity of cell-speeific effects can be resolved by considering a retinoid to be merely an effector that closes a cellular switeh. It is likely that there are cellular receptors (yet to be defined) for retinoids somewhere within the cell or on the cell surface. More than one set of critical receptors may exist for biologically active retinoids. These hypothetical... 

Layers of conducting polymers promote electron transfer. This is useful if the critical receptor process is a redox reaction. Such layers are utilized preferably in electrochemical biosensors with enzymes which catalyse biochemical redox reactions. Conducting polymers possess the advantages of classical polymers (solvent function and compatibility with organic substances) as well as of semiconductors or metals (conductance). Examples are discussed in the chapters dealing with biosensors. 

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