Adenosine Deaminase Interacts with A₁ Adenosine Receptors in Pig Brain Cortical Membranes

Abstract

Adenosine deaminase is an enzyme of purine metabolism that has largely been considered to be cytosolic. A few years ago, adenosine deaminase was reported to appear on the surface of cells. Recently, it has been demonstrated that adenosine deaminase interacts with a type II membrane protein known as either CD26 or dipeptidylpeptidase IV. In this study, by immunoprecipitation and affinity chromatography it is shown that adenosine deaminase and A1 adenosine receptors interact in pig brain cortical membranes. This is the first report in brain demonstrating an interaction between a degradative ectoenzyme and the receptor whose ligand is the enzyme substrate. By means of this interaction adenosine deaminase leads to the appearance of the high‐affinity site of the receptor, which corresponds to the receptor‐G protein complex. Thus, it seems that adenosine deaminase is necessary for coupling A1 adenosine receptors to heterotrimeric G proteins.

The Two-State Dimer Receptor Model: A General Model for Receptor Dimers

“…Because no improvement (P Ͼ 0.30; probability of less than 70%) is obtained with one extra Fig. 2, to different models Nonspecific binding was determined in the presence of an excess of (R)-PIA as described in Saura et al (1996). The determined value for nonspecific binding was 0.029 pmol/mg protein/nM.…”

International Union of Basic and Clinical Pharmacology. LXXXI. Nomenclature and Classification of Adenosine Receptors—An Update

“…Attempts have been made to assess the affinity of endogenous adenosine at A 1 receptors by examining the binding of another agonist in the presence or absence of adenosine deaminase (Cohen et al, 1996), but adenosine deaminase is a low-K m enzyme, and A 1 receptors may also interact with it in other ways (e.g., Saura et al, 1996), and the estimate is uncertain. There have also been other attempts to indirectly estimate the binding affinity of adenosine, including an attempt to partly denature the receptor by urea and disrupting interactions with the G protein (May et al, 2005).…”

Molecular Mechanisms and Therapeutical Implications of Intramembrane Receptor/Receptor Interactions among Heptahelical Receptors with Examples from the Striatopallidal GABA Neurons

“…Finally A 1 receptors colocalized with ADA on cell membranes, including cell surface cortical neurons (primary culture; Ruiz et al, 2000). The binding of ADA to the A 1 receptors appears to be essential for the high-affinity agonist binding of A 1 receptors, giving a functional role of this physical interaction in A 1 receptor-mediated transmission Saura et al, 1996Saura et al, , 1998. Thus, ADA has a role not only as a degradative ectoenzyme but also as an A 1 receptor activity-modulating protein.…”

“…• GCPR conformation at a given circumstance is the transient result of the chemical-physical factors acting upon the receptor and coming simultaneously from the extracellular space Saura et al, 1996Saura et al, , 1998, the membrane (Casadó et al, 1990, and the intracellular space (Sarrió et al, 2000).…”