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

Rat adipocyte plasma membranes were incubated with the A1 adenosine receptor agonist, 125I-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, Mr approx. 38,000, was specifically labeled. Reduction with 2-mercaptoethanol did not affect the apparent Mr 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 A1 adenosine receptor is a single protein of Mr approx. 38,000.