VANADATE OLIGOANIONS INTERACT WITH THE PROTON EJECTION BY THE CA2-RETICULUM( PUMP OF SARCOPLASMIC)

Decameric vanadate differs from other oligomeric vanadate species in i nhibiting Ca2+ uptake and H+ ejection promoted by sarcoplasmic reticul um ATPase. A decavanadate solution, 2 mM in total vanadium, containing about 200 mu M decameric species; inhibits by about 50% the uptake of Ca2+ and by 75% the H+ ejection, whereas 2 mM nominal monovanadate sl ightly increases the uptake of Ca2+ and inhibits the ejection of H+ by 25%. Moreover, decavanadate linearly increases the Ca2+/H+ ratio, whe reas monovanadate mimicks decavanadate behavior only at concentrations up to 1.2 mM. For higher concentrations of monovanadate, this effect is reversed probably due to the formation of metavanadates, namely tet ravanadate. It is concluded that Ca2+ uptake is tightly coupled to pro ton ejection through molecular events that are sensitive to the intera ction of vanadate species. Apparently, the stoichiometry is variable a nd modulated by molecular events involved in vanadate interaction sugg esting alterations in the energetic coupling associated with Ca2+ tran slocation. (C) 1994 Academic Press, Inc.