Characterization of a spectrophotometric assay for cAMP phosphodiesterase

The hydrolysis of cAMP can be monitored spectrophotometrically through the conversion of 5' AMP to 5' IMP using a specific 5' AMP amino-hydrolase (EC3.5.4.6). The optical properties and extinction coefficient differences of these compounds have been quantitatively determined. Phosphodiesterase assayed in this manner is linear with respect to time and enzyme concentration, and is more reliable than conventional assay procedures. Due to the high specificity of the assay system phosphodiesterase can be selectively assayed in unfractionated cytosol. The assay, when conducted on a conventional spectrophotometer, can detect the hydrolysis of 0.5 nmoles cAMP per min.