POLY(L-ASPARTATE) INHIBITS THE PROTON-PUMPING OF TONOPLAST H-ATPASE FROM CORN ROOTS()

Pre-incubation of the tonoplast vesicles from corn roots with poly(L-a sparate) (MW 14,000 Da) significantly inhibited the proton pumping ass ociated with the ATP hydrolysis activity of the H+-ATPase. However, th is polyanion only slightly affected the hydrolytic activity. The poten cy of poly(L-asparate) to inhibit the proton pumping increased as the concentration of KCl or ionic strength decreased suggesting an electro static origin for the inhibition. When poly(L-asparate) was added afte r the initiation of the ATPase activities, no significant effect on pr oton pumping was noted. The results suggest that certain- NH3+ groups on the cytoplasmic surface of the tonoplast membrane may electrostatic ally interact with poly(L-aspartate) to produce observed inhibition. F urthermore, the accessibility of these -NE(3+) groups to poly(L-aspart ate), appears to be regulated by the functional state of the H+-ATPase .