Diverse roles of single membrane organelles: Factors establishing the acid lumenal pH¹

Eukaryotic cells have developed an array of endomembrane systems that have differentiated to carry out various functions. They are involved in the pathways of endocytosis and exocytosis, and have an acidic lumenal pH ranging from 4.5 to 6.5. This review describes recent studies on the animal cell organelles and how they relate to the well studied systems of yeast. We focus mainly on (i) the primary proton pump (vacuolar type H⁺-ATPase) and other factors that establish acidic pH, and (ii) functions of the organelles as related to lumenal acidity.