Receptor ligand layer

Information may be stored in the architecture of the receptor, in its binding sites, and in the ligand layer surrounding the bound substrate such as specified in Table 1. It is read out at the rate of formation and dissociation of the receptor—substrate complex (14). The success of this approach to molecular recognition ties in estabUshing a precise complementarity between the associating partners, ie, optimal information content of a receptor with respect to a given substrate. 

In this model, OBPs participate in the selective transport of pheromone and other semiochemicals to their olfactory receptors. The selectivity of the system is likely to be achieved by layers of filters [ 16], i.e., by the participation of compartmentalized OBPs and olfactory receptors. It seems that OBPs transport only a subset of compounds that reach the pore tubules. Some of these compounds may not bind to the receptors compartmentalized in the particular sensilla. The odorant receptors, on the other hand, are activated by a subset of compounds, as indicated by studies in Drosophila, showing that a single OR is activated by multiple compounds [66]. If some potential receptor ligand reaches the pore tubules but are not transported by OBPs, receptor firing is prevented because the receptors are protected by the sensillar lymph. In other words, even if neither OBPs nor odorant receptors (ORs) are extremely specific, the detectors (olfactory system) can show remarkable selectivity if they function in a two-step filter. 

Figure 7.27 Schematic illustration of Surface Plasmon Resonance (SPR). Incident light is normally subject to total internal reflection in the prism block except for losses due to evanescent wave penetration of the hydrogel layer at the resonant angle. Changes in resonant angle due to receptor-ligand interactions are the basis for the real time observation of molecular recognition and association/dissociation events.

Dietary and endogenous fats are carried to the target organs by different lipoproteins, i.e. chylomicrons, LDL and HDL. These particles contain a core of TAG liposoluble vitamins and cholesteryl esters, surrounded by a phospholipid and free cholesterol layer. These also contain, by the way, specific proteins, called apolipoproteins (apo) which act as enzyme cofactors or receptor ligands. Exogenous fat is transported in chylomicrons from the intestinal epithelium to the peripheral cells, reaching the bloodstream via flie lymphatic system [11],... 

The molecular surface of receptor site regions cannot be derived from the structure infoi mation of the molecule, bth represents the form ofthe active site of a protein surrounded by a ligand. This surface representation is employed in drug design in order to illustrate the volume of the pocket region or the molecular interaction layers [186. ... 

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