Two distinct adenosine-sensitive sites on adenylate cyclase.

Abstract

The effects of adenosine and adenosine analogs on adenylate cyclases from several tissues [rat liver, I-10 Leydig tumor cell, Y-1 mouse adrenal tumor beef thyroid and human platelet membranes] were examined. Two adenosine-reactive sites were identified: the R site, occupancy of which usually leads to activation of cyclase and which requires integrity of the ribose ring for activity, and the P site, which mediates inhibition and requires integrity of the purine ring for activity. Biphasic effects of adenosine are explained by the presence of both sites on a single adenylate cyclase. Comparison of these data with those in the literature indicates that adenosine-reactive P and R sites are present generally.