Enzymatic Hydrolysis of Adenosine 3',5'-Phosphoric Acid

Abstract

During recent years the work of Sutherland and his associates (l-3) on the liver phosphorylase system has done much to clarify the mechanism of epinephrine-induced hyperglycemia. These workers have shown that epinephrine stimulates glycogenolysis by increasing the level of active phosphorylase in dog liver slices (3, 4) and in cell-free homogenates (5). The effect of epinephrine was shown to be mediated through the formation of a heatstable factor (5) which was isolated and characterized as adenosine 3’) 5’-phosphoric acid (6). Cyclic 3,5-AMP’ has been recently synthesized in high yield by a relatively simple procedure (7). Cyclic 3,5-GMP, cyclic 3,5-UMP, and cyclic 3,5CMP have also been prepared. It is not known whether these latter compounds exist physiologically. Cyclic 3,5-AMP is not confined to liver since it has been identified in particulate preparations of dog heart, skeletal muscle, and brain (8). This fact suggests that other physiological actions of epinephrine, such as cardiovascular effects and effects on smooth muscle may be related to the formation of cyclic 3,5-AMP. Sutherland and Rall (6) have briefly described an enzyme, presumably a diesterase, that hydrolyzes cyclic 3,5-AMP to 5’-AMP. The enzyme was found in brain, heart, and liver. This paper describes some of our studies on the conversion of cyclic 3,5-AMP to 5’-AMP by a diesterase present in various tissues. A convenient optical assay is described together with studies of substrate specificity, metal requirement, and inhibitors. The hydrolysis of nucleoside 2’,3’-cyclic phosphates by an enzyme in brain is also described.