title: Extracellular hydrolysis of diadenosine polyphosphates, ApnA, by bovine chromaffin cells in culture.
abstract: An ectoenzyme hydrolyzing diadenosine polyphosphates (ApnA) to AMP and Ap(n-1) has been studied in cultured chromaffin cells from bovine adrenal medulla. The KM value for extracellular Ap4A hydrolysis was 2.90 +/- 0.72 microM, the V(max) value obtained was 11.59 +/- 0.92 pmol/min x 10(6) cells (116 pmol/min.mg total protein). Ap3A, Ap5A, Ap6A, and Gp4G were competitive inhibitors of Ap4A hydrolysis with K(i) values of 3.65, 1.10, 1.20, and 2.65 microM, respectively. Phosphatidylinositol-specific phospholipase C removes the ApnA hydrolase activity from cultured chromaffin cells, suggesting an anchorage of this protein to the plasma membrane through the phosphatidylinositol. The turnover time for this enzyme calculated in the presence of cycloheximide was 38.94 +/- 1.53 hr for cultured chromaffin cells.
authors.affiliation: Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense de Madrid, Spain.
authors.forename: F
authors.initials: F
authors.lastname: Rodriguez-Pascual
authors.forename: M
authors.initials: M
authors.lastname: Torres
authors.forename: P
authors.initials: P
authors.lastname: Rotllán
authors.forename: M T
authors.initials: MT
authors.lastname: Miras-Portugal
mesh_terms: D017766:Acid Anhydride Hydrolases; D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003513:Cycloheximide / Q000494:pharmacology; D015226:Dinucleoside Phosphates / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D015226:Dinucleoside Phosphates; C020733:diadenosine tetraphosphate; D003513:Cycloheximide; D010744:Phosphoric Monoester Hydrolases; D017766:Acid Anhydride Hydrolases; C075829:diadenosine polyphosphate hydrolase