INTERACTION OF NATIVE 5'-ATP WITH PLASMA-MEMBRANES OF RAT-LIVER AND ADIPOSE-TISSUE

Studies were carried out to evaluate binding of native 5'-ATP to rat l iver and adipose plasma membranes. For this purpose excess sodium EDTA (40 mM) was used for complete inhibition of ATPase activity and stabi lization of ATP-binding. Comparative analysis of [H-3]ATP displacement by other nucleotides (ADP, AMP, GTP, GMP) revealed that only ADP is i n equimolar competition with ATP for its binding sites. Adenosine and beta-glycerophosphate had no significant effect on [H-3]ATP binding to membranes. The graphical representation of [H-3]ATP binding data in S catchard coordinates was linear, indicating the existence of single AT P-binding sites with K-d about 50-60 nM and B-max 5-7 pmoles/mg protei n. It is suggested that the interaction of extracellular ATP with plas ma membranes is realized through a ''single site-multiple function'' m echanism and includes the sequential interaction of ATP with specific nucleotide-binding sites, modulation of cellular metabolism via P-2 pu rine receptors, and finally ATP hydrolysis by a membrane ecto-ATPase.