A highly potent and selective inhibitor of vacuolar H+-ATPases (V-ATPases) in vitro. It is effective in nanomolar concentrations in animal cells, plant cells and microorganisms; also selective over other ATP hydrolyzing enzymes such as F-ATPases, Ca2+-ATPases, Na+/K+-ATPases and plasma membrane H+-ATPases. Also prevents autophagy at a late stage by inhibiting fusion between autophagosomes and lysosomes.