Vanadyl (VO2+) and vanadate (VO-3) ions inhibit the brain microsomal Na,K-ATPase with similar affinities. Protection by transferrin and noradrenaline.
The activity of Na,K-ATPase was measured in brain microsomes as the function of increasing concentrations of vanadyl (VOSO4, V4+) and the vanadate (NaVO3, V5+) ions. Both forms of vanadium inhibited the Na,K-ATPase activity with high affinity -Ki (vanadate) = 3 X 10(-7)M and Ki (vanadyl = 1 X 10(-6)M. The stability of V4+ in ATPase reaction media (Tris buffers) was measured by electron spin resonance spectroscopy. Without any reducing agent, V4+ was quickly oxidised by atmospheric oxygen. When a reducing agent such as dithiothreitol was added, the V4+ was stable for at least 30 min and the inhibition pattern of Na,K-ATPase by V4+ was not changed. The blocking effect of V4+ in the presence of dithiothreitol was counteracted by pre-incubation with equimolar concentrations of transferrin or 100 times excess of noradrenaline. The regulation of brain Na,K-ATPase by vanadate may be represented by competition between low-capacity inhibitory binding sites localized on the enzyme molecule and high-capacity sites of intracellular proteins. Preferential binding of vanadyl to the latter type of sites will decrease the intracellular concentration of the free metal and thus eliminate the enzyme inhibition.
D000818:Animals; D001921:Brain / Q000201:enzymology*; D004229:Dithiothreitol / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D066298:In Vitro Techniques; D008861:Microsomes / Q000201:enzymology*; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D014168:Transferrin / Q000494:pharmacology; D014325:Tromethamine; D014638:Vanadates; D014639:Vanadium / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D014168:Transferrin; D014639:Vanadium; D014325:Tromethamine; D014638:Vanadates; D000254:Sodium-Potassium-Exchanging ATPase; D004229:Dithiothreitol; D009638:Norepinephrine