Histidine and subcellular pH. (a) Predicted ΔpKa per histidine imidazole, averaged over histidines in each subcellular location, is plotted against subcellular pH. The line of best fit is drawn (R2 = 0.92). (b) For each subcellular compartment, the average of calculated ΔpKa per histidine is shown, and the 5% and 95% ranked values for ΔpKa in each compartment. LYS, lysosome; VAC, vacuole; GOL, golgi; ER, endoplasmic reticulum; CYT, cytoplasm; MIT, mitochondrion; NUC, nucleus; PER, peroxisome.