Inhibition of Norepinephrine Stimulated Adenyl Cyclase by Theophylline

Abstract

THEOPHYLLINE, at a concentration of 10⁻² M, has been extensively used as an inhibitor of the enzyme phosphodiesterase, which decomposes adenosine 3′,5′-phosphate (cyclic AMP) to adenosine 5-phosphate¹. It has therefore found widespread use in the determination of the activity of adenyl cyclase which catalyses the formation of this cyclic nucleotide. A recent assay developed by Weiss and Costa² eliminates the need for theophylline by using a pool of unlabelled cyclic AMP to trap that generated from labelled ATP and to protect it from destruction by phosphodiesterase. While using this procedure to study the adenyl cyclase of rat erythrocyte ghosts, it was observed that the addition of theophylline inhibited the enzyme.