Mitochondria power the cell's recycling center

The lysosome has long been understood as an organelle defined by its acidity. The steep proton gradient maintained within its lumen, a pH of 4.5 to 5.0, is prerequisite for the activation of resident hydrolases and, by extension, for all lysosome-dependent degradation, including autophagy. This acidic luminal pH is maintained by the V-type ATPase (V-ATPase), which hydrolyzes ATP to actively pump protons into the lumen. Yet a fundamental question has lingered: where do all these protons ultimately come from? Most recently, we found a striking answer - the mitochondrion.