Potassium stimulation of corn root plasmalemma ATPase. II. H+-pumping in native and reconstituted vesicles with purified ATPase
1990
Gibrat, R. | Grouzis, J.P. | Rigaud, J. | Grignon, C.
The stimulation by K+ of the initial rate of H+-pumping by ATPase was studied in native plasmelemma (Zea mays L. var Mona) vesicles and in reconstituted vesicles with enzyme purified on glycerol gradient. In reconstitued vesicles with enzyme purified on a glycerol gradient. In reconstituted vesicles, a very high H+-pumping rate (200,000% quenching per minute per milligram protein) was obtained with 9-amino-6-chloro-2-methoxyacridine provided that the pump was short-circuited by K+-valinomycin. A constant ionic strength was used to prevent indirect stimulation by the electrostatic effects of K+ salts. Indirect stimulation on H+-pumping by the short-circulating effect of internal K+, could be abolished by using the permeant anions NO3- and Br- in native, but not in reconstituted vesciles. In both materials, half-stimulation of the H+-pumping by K+ was observed at about 5 millimolar. The same stimulation was observed when K+ was present only in the external solution or when it was present both outside and inside the vesicles. It was concluded that the stimulating effect of K+ on the H+-pumping evidenced in these experiments on both native and reconstituted vesicles was due to a direct effect of the cation on the cytoplasmic face of the ATPase. These results are discussed within the context of the hypothesis of an active K+ transport driven by the ATPase through a direct H+/K+ exchange mechanism.
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