(Na+-K+) -ATPase interaction with L-ascorbic acid. Effect on p-nitrohenylphosphatase partial reaction
Miggiano, G.A.; Martorana, G.E.; Mordente, A.; Di Bonifacio, L.; Castelli, A.
Italian Journal of Biochemistry 37(5): 284-292
1988
ISSN/ISBN: 0021-2938 PMID: 2853143 Document Number: 310691
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.