title: Subcellular distribution studies of diadenosine polyphosphates--Ap4A and Ap5A--in bovine adrenal medulla: presence in chromaffin granules.
abstract: Diadenosine tetraphosphate (Ap4A) and diadenosine pentaphosphate (Ap5A) have been identified in bovine adrenal medullary tissue using an HPLC method. The values obtained were 0.1 +/- 0.05 mumol/g of tissue for both compounds. The subcellular fraction where Ap4A and Ap5A were present in the highest concentration was chromaffin granules: 32 nmol/mg of protein for both compounds (approximately 6 mM intragranularly). This value was 30 times higher than in the cytosolic fraction. Enzymatic degradation of Ap4A and Ap5A, isolated from chromaffin granules, with phosphodiesterase produces AMP as the final product. The Ap4A and Ap5A obtained from this tissue were potent inhibitors of adenosine kinase. Their Ki values relative to adenosine were 0.3 and 2 microM for Ap4A and Ap5A, respectively. The cytosolic fraction also contains enzymatic activities that degrade Ap4A as well as Ap5A. These activities were measured by an HPLC method; the observed Km values were 10.5 +/- 0.5 and 13 +/- 1 microM for Ap4A and Ap5A, respectively.
authors.affiliation: Departamento de Bioquimica, Facultad de Medicina, Universidad de la Laguna, Islas Canarias, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Rodriguez del Castillo
authors.forename: M
authors.initials: M
authors.lastname: Torres
authors.forename: E G
authors.initials: EG
authors.lastname: Delicado
authors.forename: M T
authors.initials: MT
authors.lastname: Miras-Portugal
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000248:Adenosine Kinase / Q000037:antagonists & inhibitors; D000249:Adenosine Monophosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000263:Adenylate Kinase / Q000378:metabolism; D000313:Adrenal Medulla / Q000032:analysis / Q000378:metabolism / Q000648:ultrastructure*; D000818:Animals; D002417:Cattle; D002837:Chromaffin Granules / Q000032:analysis* / Q000378:metabolism; D002838:Chromaffin System / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000032:analysis; D015226:Dinucleoside Phosphates / Q000032:analysis* / Q000378:metabolism / Q000494:pharmacology; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism
chemical_list: D015226:Dinucleoside Phosphates; D000249:Adenosine Monophosphate; C012275:P(1),P(5)-di(adenosine-5'-)pentaphosphate; C020733:diadenosine tetraphosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000248:Adenosine Kinase; D000263:Adenylate Kinase; D010744:Phosphoric Monoester Hydrolases