Inhibitory effects of some purinergic agents on ecto-ATPase activity and pattern of stepwise ATP hydrolysis in rat liver plasma membranes

摘要: Inhibitory effects of various purinergic compounds on the Mg 2a -dependent enzymatic hydrolysis [ 3 H]ATP in rat liver plasma membranes were evaluated. Rat enzyme ecto-ATPase has a broad nucleotide-hydrolyzing activity, displays Michaelis^Menten kinetics with Km for ATP 368 ˛ 56 WM and is not sensitive to classical inhibitors ion-exchange intracellular ATPases. P2-antagonists diadenosine tetraphosphate (Ap4A) progressively non-competitively inhibited activity following rank order inhibitory potency: suramin (pIC50, 4.570)s Reactive blue 2 (4.297)EAp4A (3.268)s pyridoxalphosphate-6-azophenyl-2P,4P-disulfonic acid (PPADS) (2.930). Slowly hydrolyzable P2 agonists ATPQS, ADPLS, K,L-methylene L,Q-methylene as well polyphosphates Ap3A Ap5A did exert any at concentration ranges 10 34 ^10 33 M. Thin-layer chromatography analysis formation metabolites indicated presence other activities surface (ecto-ADPase 5P-nucleotidase), participating concert nucleotide through stepwise reactions ATPCADPCAMPCadenosine. A similar pattern sequential dephosphorylation still occurs suramin, Ap4A PPADS, but appearance ultimate reaction product, adenosine, was significantly delayed. In contrast, only followed ATPCADP, subsequent AMP adenosine being virtually eliminated. These data suggest that although nucleotide-binding sites are distinct from those receptors, some antagonists can potentiate cellular responses extracellular non-specific inhibition ensuing pathways purine catabolism. fl 2000 Elsevier Science B.V. All rights reserved.