title: (Na+-K+)-ATPase interaction with L-ascorbic acid. Effect on p-nitrohenylphosphatase partial reaction.
abstract: L-ascorbic acid preincubation with rabbit kidney (Na+-K+)-ATPase inhibits the activity of p-nitrophenylphosphatase partial reaction with a pseudo-first order decay. The presence of the pseudosubstrate, p-nitrophenylphosphate, counteracts the inhibiting effect. During the reaction course, the kinetic rate is enhanced at ascorbic acid concentrations below 0.7 mmol/1, but is inhibited above that amount. The intrinsic fluorescence of the enzyme in E1 and E2 conformations is modified suggesting the occurrence of ascorbate-induced intermediate forms, distinct from those provoked by the addition of cations, magnesium and phosphate. These destabilized forms appear easier to be converted into catalytically active or increasingly inhibited states.
authors.affiliation: Istituto di Chimica Biologica, Facoltà di Medicina e Chirurgia, Università Cattolica del S. Cuore, Roma.
authors.forename: G A
authors.initials: GA
authors.lastname: Miggiano
authors.forename: G E
authors.initials: GE
authors.lastname: Martorana
authors.forename: A
authors.initials: A
authors.lastname: Mordente
authors.forename: L
authors.initials: L
authors.lastname: Di Bonifacio
authors.forename: A
authors.initials: A
authors.lastname: Castelli
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors*; D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D007668:Kidney / Q000201:enzymology; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors*; D011480:Protease Inhibitors / Q000494:pharmacology; D011817:Rabbits; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D011480:Protease Inhibitors; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D001205:Ascorbic Acid