The literature concerning the following topics has been reviewed.
1) Techniques of quantifying the binding of ligands to β-adrenergic receptors.
2) The relationship between structure of ligands and their ability to bind to the β-adrenergic receptor.
3) The relationship between structure of ligands and their ability to activate subsequent physiological phenomena once bound (i.e. their intrinsic activity).
4) The physical and chemical properties of the β-adrenergic receptor.
A radioactively labelled ligand, 1-(2-iodophenoxy)-3-isopropylamino-2-propanol (IIPP), which binds with high affinity to the β-adrenergic receptor has been synthesized and resolved into its active and inactive stereoisomers. Its interaction with avian erythrocyte β-adrenergic receptors has been characterized.
A novel, competitive binding assay has been developed to measure association of ligand with particulate receptors under true equilibrium conditions. As the concentration of free and bound labelled ligand is determined in the assay mixture, the effect of a range of competing ligand concentrations can be measured using a single particulate receptor sample by sucessive additions of competing ligand. The technique is economical and can achieve a high accuracy because sampling errors are avoided.
The theory of competitive binding has been examined and new methods developed for establishing association constants and receptor concentrations. The methods eliminate the need to determine nonspecific binding, do not require a constant free ligand concentration, and permit the computation of free unlabelled ligand concentration in situations where there is a significant quantity thereof. These situations are major sources of errors in the analysis of binding data using conventional methods.
Preliminary experiments are reported which are directed towards
1) determining 3-adrenergic receptor quantities and class on individual cells by quantitative autoradiography,
2) finding suitable affinity chromatography ligands for isolating cells with high levels of β-adrenergic receptors.
An investigation into the probable conformation of bound β-adrenergic ligands has been carried out using molecular models to determine the set of possible conformations common to known high affinity ligands. This set was found to be severely limited, on the basis the currently proposed structures based on the prefered solution conformations of arylethanolamines and aryloxypropanolamines appear to be erroneous. A model based on the common conformation has been proposed which is able to explain most structure-activity relationships.