A CHARACTERIZATION OF PERVANADATE, AN INDUCER OF CELLULAR TYROSINE PHOSPHORYLATION AND INHIBITOR OF GAP JUNCTIONAL INTERCELLULAR COMMUNICATION

Gap junctional intercellular communication (GJIC), phosphorylation sta tus of the gap junction protein, connexin43 (Cx43), and cellular tyros ine phosphorylation in Syrian hamster embryo cells have been employed for a biological characterization of pervanadate (a mixture of H2O2 an d vanadate), In addition, electron paramagnetic resonance (EPR) spectr oscopy was used to follow the appearance and disappearance of vanadyl (V(IV)), It has previously been suggested that pervanadate is vanadyl hydroperoxide (V-(4+)OOH), This assumption was tested by using mixture s with different molar ratios of H2O2 and orthovanadate, metavanadate or vanadyl sulfate. The maximal biological activity of the mixtures we re found at a molar ratio of 2:1 (H2O2:orthovanadate or metavanadate) or 2.5:1 (H2O2:alkaline vanadyl sulfate). No V(TV) EPR spectrum appear ed upon mixing orthovanadate or metavanadate and H2O2. The V(IV) EPR s pectrum disappeared when vanadyl sulfate was incubated with H2O2 in a 0.5:1 molar ratio (H2O2:alkaline vanadyl sulfate), Spectrophotometrica lly, a V(V)-like peak at 265 nm had its optimum at this ratio. These r esults are consistent with pervanadate being diperoxovanadate. The ind ividual compounds were prominently less active than the per-compound m ixtures in affecting the biological parameters, The decreases in GJIC showed a concentration-dependent correlation with the onset of the alt erations of the Cx43 band pattern and the amount of phosphotyrosine in cellular proteins, but the correlation was not absolute. All the stud ied biological parameters were reversible, also under continuous expos ure to pervanadate.