Binding Characteristics of 3H-Dihydroalprenolol to β-Adrenergic Receptors of Rat Brain: Influence of Exo- and Endo-Glycosidases and Glycopeptidase

Abstract

The significance of carbohydrate moieties containing the β-adrenoceptor molecule in the rat brain was examined using radioligand binding assay methods. Thus, this experiment was designed to assess the effects of exoglycosidase (α-D-mannosidase and neuraminidase), endoglycosidase (endoglycosidase D and endoglycosidase H), and glycopeptidase A on the affinity of β-adrenoceptor. The main reason why five kinds of enzymes were used in the present study is that they can hydrolyze different carbohydrate molecules from cell membranes. Rat brain was used and β-adrenoceptor binding assay was carried out using 3H-dihydroalprenolol (3H-DHA) as a ligand. 3H-DHA binding to β-adrenoceptors was sensitive to very low concentration of endoglycosidase H and glycopeptidase A, thus indicating that the treatments with these enzymes of rat brain membrane appear to decrease the number of β-receptor binding sites. On the other hand, the treatment with neuraminidase, endoglycosidase H, and glycopeptidase A of the membrane induced lower values of the dissociation constant (Kd) than those of the control, α-D-mannosidase and endoglycosidase D are without effect in spite of the removal of hexose contents and total carbohydrate contents with these treatments, respectively. These results imply that complex type N-linked acidic carbohydrate chains containing neuraminic acid and high mannose type N-linked carbohydrate chains, which are hydrolyzed with endoglycosidase H and glycopeptidase A, of the rat brain membrane containing β-adrenoceptor molecules play a crucial role in the drug-receptor interaction.