VANADIUM-DIASCORBATES ARE STRONG CANDIDATES FOR ENDOGENOUS OUABAIN-LIKE FACTORS IN HUMAN URINE - EFFECTS ON NA-K-ATPASE ENZYME-KINETICS

Recently, we isolated from the urine of salt-loaded healthy subjects a more like factor OLF-1 and a more apolar OLF-2, the latter cross-reac ted with a digoxin anti-body. They were purified to single compounds w ith dose-dependent Na-K-ATPase inhibition. Mass-spectroscopy (MS) show ed a M(r) of around 400 and H-1-NMR- and IR-spectroscopy suggested dia scorbic acid salts, i.e., vanadium (V) diascorbates (M(r) 403) with si milar elution times from RP-HPLC as OLFs. IC50 was 9 x 10(-5)M for V-I V-diascorbate as compared to 2 x 10(-6)M for V-V-diascorbate. Enzyme i nhibition was non-competititive with respect to sodium and Mg-ATP; p-N PPase assay showed strong inhibition in its E2-configuration. We sugge st that V-diascorbates represent endogenous OLFs excreted in human uri ne. (C) 1995 Academic Press, Inc.