title: Kinetics of Na+, K+-ATPase inhibition by an endogenous modulator (II-A).
abstract: We have previously reported the isolation by gel filtration and anionic exchange HPLC of two brain Na+, K+-ATPase inhibitors, II-A and II-E, and kinetics of enzyme interaction with the latter. In the present study we evaluated the kinetics of synaptosomal membrane Na+, K+-ATPase with II-A and found that inhibitory activity was independent of ATP (2-8 mM), Na+ (3.1-100 mM), or K+ (2.5-40 mM) concentration. Hanes-Woolf plots showed that II-A decreases Vmax in all cases; KM value decreased for ATP but remained unaltered for Na+ and K+, indicating respectively uncompetitive and noncompetitive interaction. However, II-A became a stimulator at 0.3 mM K+ concentration. It is postulated that brain endogenous factor II-A may behave as a sodium pump modulator at the synaptic region, an action which depends on K+ concentration.
authors.affiliation: Instituto de Biología Celular y Neurociencias, Prof. Eduardo De Robertis, PROBICENE-CONICENT, Facultad de Medicina, Universidad de Buenos Aires, Argentina.
authors.forename: A
authors.initials: A
authors.lastname: Reinés
authors.forename: C
authors.initials: C
authors.lastname: Peña
authors.forename: G
authors.initials: G
authors.lastname: Rodríguez de Lores Arnaiz
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000302:isolation & purification / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D013574:Synaptosomes / Q000201:enzymology*
chemical_list: D004791:Enzyme Inhibitors; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium