Inhibition of the vacuolar ATPase of Acer pseudoplatanus cells by vanadate.

Unlike most tonoplast ATPases, the vacuolar ATPase of Acer pseudoplatanus cells (Km = 0.4 mM) was strongly inhibited by vanadate (I50 = 10 microM). The inhibition was non-competitive. Chemicals usually added in the reaction mixture either increase (NH+4, K+) or decrease (Na+, EDTA) the ATPase inhibition. However, these results do not explain the insensitivity to vanadate of most tonoplast ATPases. We suggest that the tonoplast contains 2 classes of ATPases, one sensitive to vanadate, the other insensitive; each class should be more or less abundant (or active) according to the plant species studied or its physiological state of growth. It appears from this study that sensitivity or insensitivity of an ATPase to vanadate is not really a good criterion to distinguish between plasmalemma and tonoplast.