Figure 4. Constitutive Functions of The Yeast Vacuole.

The vacuole is responsible for multiple constitutive processes: 1) degradation, 2) storage, 3) buffering, and 4) detoxification. 1) Degradation: The vacuole is highly enriched for hydrolases (yellow circles) that break down cargo delivered via multiple trafficking pathways to the vacuole. 2) Storage: The vacuolar membrane contains multiple transporters (blue polygons) that import amino acids, ions, and metals. Vacuolar acidification by the vacuolar H⁺ ATPase (V₁ and V₀, green) is required for proper maturation of hydrolases and for establishing the proton gradient that drives many transporters. 3) Buffering: The vacuolar membrane also contains transporters that recycle amino acids, ions, and metals to the cytosol. The combined activity of importers and exporters is important for ion homeostasis and amino acid recycling. The vacuole is also the main storage site for polyphosphate which buffers cations and is a source for cellular phosphate, 4) Detoxification: The vacuole also sequesters toxic metals and potentially harmful metabolic bi-products via ABC transporters.