A GTP-binding protein required for secretion rapidly associates with secretory vesicles and the plasma membrane in yeast

The proton-translocating ATPase of the fungal plasma membrane☆

The effects of vanadate, molybdate, and azide on ATP phosphohydrolase (ATPase) and acid phosphatase activities of plasma membrane, mitochondrial, and soluble supernatant fractions from corn ( Zea mays L. WF9 × MO17) roots were investigated. Azide (0.1-10 millimolar) was a selective inhibitor of pH 9.0-ATPase activity of the mitochondrial fraction, while molybdate (0.01-1.0 millimolar) was a relatively selective inhibitor of acid phosphatase activity in the supernatant fraction. The pH 6.4-ATPase activity of the plasma membrane fraction was inhibited by vanadate (10-500 micromolar), but vanadate, at similar concentrations, also inhibited acid phosphatase activity. This result was confirmed for oat ( Avena sativa L.) root and coleoptile tissues. While vanadate does not appear to be a selective inhibitor, it can be used in combination with molybdate and azide to distinguish the plasma membrane ATPase from mitochondrial ATPase or supernatant acid phosphatase. Vanadate appeared to be a noncompetitive inhibitor of the plasma membrane ATPase, and its effectiveness was increased by K + . K + -stimulated ATPase activity was inhibited by 50% at about 21 micromolar vanadate. The rate of K + transport in excised corn root segments was inhibited by 66% by 500 micromolar vanadate.

C W Slayman

Papers

The effects of vanadate on the plasma membrane ATPase of Neurospora crassa.