PROPERTIES OF PERVANADATE AND PERMOLYBDATE - CONNEXIN43, PHOSPHATASE INHIBITION, AND THIOL REACTIVITY AS MODEL SYSTEMS

Pervanadate and permolybdate are irreversible protein-tyrosine phospha tase inhibitors, with IC50 values of 0.3 and 20 mu M respectively, in intact cells. Maximal inhibition was obtained within 1 min at higher c oncentrations of the compounds. They induced prominent changes in the phosphorylation status of the gap junction protein, connexin43. These effects were utilized as model systems to assess the stability and ina ctivation of the compounds. Although the concentrated stock solutions were relatively stable, the diluted compounds were unstable. The biolo gical activity had decreased to 20-30% after 6 h of incubation in a ph osphate buffer, 1 h in phosphate buffer with 10% fetal calf serum, and 13 minutes in culture medium. Thiols reacted rapidly with the compoun ds and inactivated them (initial reaction rates with cysteine: permoly bdate > pervanadate > H2O2). Catalase inactivated the compounds, and p ermolybdate was the more sensitive. The cells inactivated permolybdate faster than pervanadate. Cellular inactivation of permolybdate, and t o a lesser degree pervanadate, appeared to be partly dependent on cata lase and thiols. However, a general decrease in cellular thiols was no t the mediator of the biological effects of pervanadate or permolybdat e. Mathematical modeling of the thiol reactivity suggested that monope roxovanadate at maximum could possess 20% of the biological activity o f diperoxovanadate.