Two distinct proton translocating ATPases are present in membrane vesicles from radish seedlings

Two distinct systems of Mg‐ATP‐dependent transport of protons have been put in evidence in microsomal vesicles from radish seedlings by investigating the effects of vanadate and of NO− 3 on the initial rate of acridine orange accumulation. One system is vanadate‐resistant and is inhibited by NO− 3 (I 50 1.3 mM), the other is inhibited by vanadate (I 50 43 μM) and unaffected by NO− 3. The two systems differently distribute along a continuous sucrose density gradient: the NO− 3‐sensitive system of Mg‐ATP‐dependent transport of protons peaks at d = 1.13–1.14, while the vanadate‐sensitive one peaks at d = 1.16–1.17.