title: The identification and characterization of two cyclic nucleotide phosphodiesterases from bovine adrenal medulla.
abstract: Two soluble cyclic nucleotide phosphodiesterase activities, designated Peak I (Mr = 216,000) and Peak II (Mr = 230,000), have been isolated from bovine adrenal medulla by DEAE-cellulose chromatography. Peak I has Ca2+-independent, cGMP-specific phosphodiesterase activity and Peak II has cGMP-stimulated cyclic nucleotide phosphodiesterase activity. Peak I hydrolyzes cGMP with hyperbolic kinetics and demonstrates a Km of 23 microM. Peak II hydrolyzes cGMP with hyperbolic kinetics but hydrolyzes cAMP with slightly sigmoidal kinetics and demonstrates Km values of 54 +/- 0.7 microM cGMP and 38 +/- 6 microM cAMP. Cyclic AMP and cGMP are competitive inhibitors of each other's hydrolysis, suggesting that these nucleotides may be hydrolyzed at the same catalytic site. Micromolar concentrations of cGMP cause a 5-fold stimulation of the hydrolysis of subsaturating concentrations of cAMP by the Peak II phosphodiesterase. Half-maximal activation occurs at 0.5 microM cGMP and the result of activation is a decrease in the apparent Km for cAMP. Stimulation of the hydrolysis of subsaturating concentrations of cGMP by cAMP was also detected; however, cAMP is a less potent activator of the enzyme than cGMP. Cyclic AMP causes a 1.5-fold stimulation of cGMP hydrolysis and half-maximal activation occurs at 2.5 microM cAMP.
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000037:antagonists & inhibitors / Q000302:isolation & purification* / Q000378:metabolism; D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000037:antagonists & inhibitors / Q000302:isolation & purification* / Q000378:metabolism; D000313:Adrenal Medulla / Q000201:enzymology*; D000818:Animals; D002417:Cattle; D000242:Cyclic AMP / Q000494:pharmacology; D006152:Cyclic GMP / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D007700:Kinetics; D008970:Molecular Weight; D012995:Solubility; D013379:Substrate Specificity
chemical_list: D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D006152:Cyclic GMP