In 2019, Li et al. devised a 4-mer·capto·pyridine/gold nanostar probe to accurately monitor this quantity via plasmon-enhanced Raman spectroscopy. Phosphorylation of the TFEB gene increases the transcription of a 14-subunit complex crucial to lowering this quantity. Hydroxychloroquine’s (15[1])anti-autoimmune (15[1])effect in treating lupus is in part due to its ability to raise this quantity in APCs. Studies that demonstrate poly·ethyl·en·imine’s ability to stabilize this quantity support (-5[1])its role as a (*) “sponge.” Most cathepsins only function within a narrow range of this quantity. Dysfunction of the V-type ATPase that regulates this quantity leads to its increase, which in turn inhibits the function of previously mannose-6-phosphate-tagged hydrolases. For 10 points, what quantity’s normal value of 4 to (10[1])5 activates the proteolytic enzymes of a specific organelle? (10[1])■END■