title: A comparative study between a brain Na+,K(+)-ATPase inhibitor (endobain E) and ascorbic acid.
abstract: In the search of Na+,K(+)-ATPase modulators, we have reported the isolation by gel filtration and HPLC of a brain fraction, termed endobain E, which highly inhibits Na+,K(+)-ATPase activity. In the present study we compared some properties of endobain E with those of ascorbic acid. Kinetic experiments assaying synaptosomal membrane K(+)-p-nitrophenylphosphatase (K(+)-p-NPPase) activity in the presence of endobain E or ascorbic acid showed that in neither case did enzyme inhibition prove competitive in nature versus K+ or p-NPP concentration. At pH 5.0, endobain E and ascorbic acid maximal UV absorbance was 266 and 258 nm, respectively; alkalinization to pH 14.0 led to absorption drop and shift for endobain E but to absorbance disappearance for ascorbic acid. After cysteine treatment, endobain E absorbance decreased, whereas that of ascorbic acid remained unaltered; iodine treatment led to absorbance drop and shift for endobain E but to absorbance disappearance for ascorbic acid. HPLC analysis of endobain E disclosed the presence of two components: one eluting with retention time and UV spectrum indistinguishable from those of ascorbic acid and a second, as yet unidentified, both exerting Na+,K(+)-ATPase inhibition.
authors.affiliation: Instituto de Biología Celular y Neurociencias "Prof. E. De Robertis", PROBICENE-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina. grodrig@ffyb.uba.ar
authors.forename: G
authors.initials: G
authors.lastname: Rodríguez de Lores Arnaiz
authors.forename: T
authors.initials: T
authors.lastname: Herbin
authors.forename: C
authors.initials: C
authors.lastname: Peña
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001205:Ascorbic Acid / Q000494:pharmacology*; D001921:Brain / Q000187:drug effects / Q000201:enzymology*; D003545:Cysteine / Q000494:pharmacology; D007455:Iodine / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D010042:Ouabain / Q000031:analogs & derivatives* / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000975:Antioxidants; C119205:endobain E; D010042:Ouabain; D007455:Iodine; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D003545:Cysteine; D001205:Ascorbic Acid