Vacuoles are generally believed to present storage compartments for inorganic ions and a variety of organic compounds. However, studies on the mechanism of vacuolar compartmentation were indirect. and rather confusing.
In yeast Saccharomyces cerevisiae, vacuoles are the largest organelles, occupying about 25% of the total cell volume, and they are postulated to function as lysosomes and as a stomge compartment of basic amino acids, S-adenosylmethionine and polyphophates. There must exist some specific transport mechanisms in the vacuolar membranes. Recently, we established a procedure for preparing right-side-out vacuolar membrane vesicles of high purity from cells of the yeast, Saccharomyces cerevisiae, and showed that the vesicles catalyze active transport of ten amino acids and Ca²⁺ which are driven by an electrochemical potential difference of protons formed by ATP hydrolysis. Studies on ATPase activity on vacuolar membrane vesicles indicated the presence of a new type of H⁺-ATPase, which is different from mitochodrial and plasma membrane H⁺-ATPases. This vacuolar membrane ATPase was partially purified and showed entirely different subunit structure from other two ATPases.
These results suggest that vacuoles have their own energy tranducing mechanism and active transport systems, and play active roles on metabolic regulation of the cells.