title: Vanadium-diascorbates are strong candidates for endogenous ouabain-like factors in human urine: effects on Na-K-ATPase enzyme kinetics.
abstract: Recently, we isolated from the urine of salt-loaded healthy subjects a more polar ouabain-like factor OLF-1 and a more apolar OLF-2, the latter cross-reacted with a digoxin anti-body. They were purified to single compounds with dose-dependent Na-K-ATPase inhibition. Mass-spectroscopy (MS) showed a Mr of around 400 and 1H-NMR- and IR-spectroscopy suggested diascorbic acid salts, i.e., vanadium (V) diascorbates (Mr 403) with similar elution times from RP-HPLC as OLFs. IC50 was 9 x 10(-5)M for VIV-diascorbate as compared to 2 x 10(-6)M for Vv-diascorbate. Enzyme inhibition was non-competitive with respect to sodium and Mg-ATP; p-NPPase assay showed strong inhibition in its E2-configuration. We suggest that V-diascorbates represent endogenous OLFs excreted in human urine.
authors.affiliation: Department of Anatomy and Physiology, Faculty of Agricultural Sciences, University of Bonn, Germany.
authors.forename: H J
authors.initials: HJ
authors.lastname: Kramer
authors.forename: G
authors.initials: G
authors.lastname: Krampitz
authors.forename: A
authors.initials: A
authors.lastname: Bäcker
authors.forename: G
authors.initials: G
authors.lastname: Krampitz
authors.forename: H
authors.initials: H
authors.lastname: Meyer-Lehnert
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors; D000818:Animals; D001205:Ascorbic Acid / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology / Q000652:urine; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors; D002413:Cations, Divalent; D002540:Cerebral Cortex / Q000201:enzymology; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D009942:Organometallic Compounds / Q000737:chemistry / Q000494:pharmacology / Q000652:urine*; D010042:Ouabain / Q000494:pharmacology*; D012982:Sodium, Dietary; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D013055:Spectrophotometry, Infrared; D013552:Swine
chemical_list: D002413:Cations, Divalent; D009942:Organometallic Compounds; D012982:Sodium, Dietary; C095018:vanadium diascorbate; D010042:Ouabain; D009597:4-Nitrophenylphosphatase; D017301:Ca(2+) Mg(2+)-ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D001205:Ascorbic Acid