Occupancy binding studies

Figure 13.6 Structures of two radiotracers used for occupancy binding studies in the central nervous system...

The interaction of ACh with the Torpedo nAChR. The data shown compare the equilibrium binding parameters obtained from fluorescence studies using covalently attached fluorescent probes and those obtained from radiolabelled [ H]ACh binding studies or functional measurements of cation flux. These data support a model in which the Torpedo nAChR carries sites of different affinities for ACh. We have previously suggested that occupancy of the lower affinity sites leads to channel activation whereas the higher affinity sites may play a role in desensitization processes... 

Half-maximal effects for insulin stimulation of the receptor tyrosyl kinase occurred at around 5-10 nM insulin and, from analysis of insulin specific-binding studies, it appears that there is a non-linear relationship between the stimulation of receptor autophosphorylation by insulin and receptor occupancy. In contrast, a linear relationship has been noted between steady-state insulin binding and the ability of solubilized receptor kinase preparations to phosphorylate various exogenous substrates. The kinetics of coupling between insulin binding and the ability to elicit kinase activation as regards both exogenous substrates and its autophosphorylative capability requires further study. 

Gratifyingly, the compounds were characterized by a markedly reduced volume of distribution (Vdss) in comparison to dibasic analogs (2-8 instead of 200-400 1/ kg). When evaluated in ex vivo binding studies on rat cerebral cortex to measure central H3 receptor occupancy, compounds 27 and 30 showed moderate but acceptable brain penetration (63 and 43% H3 brain receptor occupancy on rat cortex homogenate 1 h after intraperitoneal (i.p.) administration of 1 mg/kg of 27 and 30, respectively). 

Fig. 4 Diagram of the electron energy levels with their maximum occupancy binding energy of the XPS peaks for elements that are of interest in the study of Wosystems and biomaterials bold) and can be analyzed with the commercial spectrometers energy of other Is levels italic), and sketch of the transitions responsible for the Kai and Ka2 X-ray lines " ...

Apart from its natural occurrence, Co may find its way into other proteins either adventitiously or deliberately. A study was undertaken where the blood, serum, and plasma of workers occupationally exposed to Co were analyzed for the element.1189 When separated by gel electrophoresis under denaturing conditions, the Co fractions in all blood, serum, and plasma samples showed a similar protein pattern. A variety of proteins of differing size were found to bind Co in fractions collected at pFl 5, whereas only hemoglobin was found in the pH 7 fractions. The conclusions were that in vivo Co is bound to plasma proteins, perhaps albumin and hemoglobin. 

---