Photochemical cross-linking of 125I-hydroxyphenylisopropyl adenosine to the A1 adenosine receptor of rat adipocytes

Abstract Rat adipocyte plasma membranes were incubated with the A 1 adenosine receptor agonist, 125 I-hydroxyphenylisopropyl adenosine (1 nM) and then treated with the photoactive cross-linking agent, ANB-NOS. The membranes were solubilized and analyzed by SDS-PAGE and autoradiography. A single protein, M r approx. 38 000, was specifically labeled. Reduction with 2-mercaptoethanol did not affect the apparent M r of the labeled protein. Labeling was inhibited by the adenosine receptor agonists, HPIA, PIA and NECA, and by the antagonist, theophylline, but was unaffected by inosine. We conclude that the A 1 adenosine receptor is a single protein of M r approx. 38 000.