Reconstitution of a proton pump from gastric mucosa

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Abstract
Purified vesicular fractions from hog gastric mucosa have been incorporated into phosphatidyl serine bilayers. In the presence of MgATP on one side and symmetrical Na2SO4 solutions, a short circuit current (SCC) away from that side is observed increasing exponentially with time, while the corresponding open circuit potential (OCP) is maintained constant for >30 min. In K2SO4 solutions the SCC time course is essentially unchanged, but the OCP falls to almost zero after 15–20 min. In Na−K gradient there is a similar SCC away from the K-side whose exponential rate is increased by ATP added to both sides. The time course of these events depends only on the time from the formation of the black film. These results are interpreted as showing: (1) There is an ATP-driven proton pump generating a constant potentialE H in series with a time dependent conductanceg H ∝ e kt . (2) There is a shunting K-conductanceg K ∝ e k't . (3) In the presence of ATPk'>k. (4) This time dependence is due to thickness changes in the bilayer. A model relates these results to those obtained with the intact vesicles.