title: Studies on adenosine 3',5'-monophosphate phosphodiesterase of human erythrocyte membranes.
abstract: In this work we show the existence of cyclic AMP phosphodiesterase (EC 3.1.4.17) in human erythrocyte membranes and have clarified some properties of the enzyme. In human erythrocytes, about 23% of the total cyclic AMP phosphodiesterase activity is in a membrane-bound form. Although it could be solubilized with Triton X-100 in 5 mM Tris-HCl buffer (pH 8.0), it was not solubilized by a low or high concentration of salt. The enzyme seems to be localized in the cytoplasmic surface, since it is detected in sealed inside-out vesicles of human erythrocyte membranes, but not in intact human erythrocytes. The optimum pH was found to lie between 7.4 and 8.0, and Mg2+ was found to be necessary for its activity. Ca2+ and calmodulin could not stimulate the activity of this enzyme. Theophylline was a strong inhibitor, but cyclic GMP could not inhibit the enzymic hydrolysis of cyclic [32P]AMP and this membrane-bound enzyme therefore seems to be specific to cyclic AMP.
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000097:blood*; D003593:Cytoplasm / Q000201:enzymology; D004910:Erythrocyte Membrane / Q000201:enzymology*; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D017830:Octoxynol; D011092:Polyethylene Glycols / Q000494:pharmacology
chemical_list: D011092:Polyethylene Glycols; D017830:Octoxynol; D015105:3',5'-Cyclic-AMP Phosphodiesterases