Poly(L‐aspartate) inhibits the proton pumping of tonoplast H⁺‐atpase from corn roots

Abstract

Pre‐incubation of the tonoplast vesicles from corn roots with poly(L‐aspartate) (MW 14,000 Da) significantly inhibited the proton pumping associated with the ATP hydrolysis activity of the H⁺‐ATPase. However, this polyanion only slightly affected the hydrolytic activity. The potency of poly(L‐aspartate) to inhibit the proton pumping increased as the concentration of KCl or ionic strength decreased suggesting an electrostatic origin for the inhibition. When poly(L‐aspartate) was added after the initiation of the ATPase activities, no significant effect on proton pumping was noted. The results suggest that certain‐ NH³⁺ groups on the cytoplasmic surface of the tonoplast membrane may electrostatically interact with poly(L‐aspartate) to produce observed inhibition. Furthermore, the accessibility of these ‐NH³⁺groups to poly(L‐aspartate), appears to be regulated by the functional state of the H⁺‐ATPase.

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