title: Ecto-diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A)-hydrolase is expressed as an ectoenzyme in a variety of mammalian and human cells and adds new aspects to the turnover of Ap4A.
abstract: Ap4A and other dinucleotides participate in the regulation of hemostasis and blood pressure control. With the exception of two previously reported surface anchored ectoAp4A-hydrolases on bovine aortic endothelial and chromaffine cells, all Ap4A-hydrolases reported are intracellular or freely soluble. We demonstrated that ectoAp4A-hydrolases are present on a broad variety of cell types of different species: rat mesangial, bovine corneal epithelial, human Hep-G2 and peridontal cells. Ectoenzyme properties were evaluated on rat mesangium cells. Chromatography of purified plasma membranes on Sephacel 300 resulted in enrichment of ectoAp4A-hydrolase and in separation from ectoATPase. In contrast to ATPase, Ap4A-hydrolase was stable at room temperature. EctoAp4A-hydrolase also recognized ATP as substrate, and therefore is not highly specific. The molecular weight was 180 kD. Unlike ectoAMPase ectoAp4A-hydrolase was not attached via a glycosyl-phosphatidylinositol (GPI)-moiety. Concentrations of PI-PLC 10-100-fold higher than effective for ectoAMPase cleavage (10-100 mU/ml) plus extensively extended incubation times up to eight hours did not result in cleavage of ectoAp4A-hydrolase. The enzyme ectoAp4A-hydrolase might presage a direction for pharmaceutical manipulation in the control of blood pressure and hemostasis.
authors.affiliation: The Blood Center of Southeastern Wisconsin, Blood Research Institute, Milwaukee 53226-2178, USA. avdrygalski@bcsew.edu
authors.forename: A
authors.initials: A
authors.lastname: von Drygalski
authors.forename: A
authors.initials: A
authors.lastname: Ogilvie
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000378:metabolism*; D000818:Animals; D001011:Aorta; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000201:enzymology / Q000378:metabolism*; D015226:Dinucleoside Phosphates / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000201:enzymology / Q000378:metabolism*; D019573:Epithelium, Corneal / Q000201:enzymology / Q000378:metabolism*; D005920:Glomerular Mesangium / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D010519:Periodontium / Q000201:enzymology / Q000378:metabolism; D051381:Rats; D014407:Tumor Cells, Cultured
chemical_list: D015226:Dinucleoside Phosphates; C020733:diadenosine tetraphosphate; D017766:Acid Anhydride Hydrolases; C020023:bis(5'-nucleosyl)tetraphosphatase (asymmetrical)