Histidine location and subcellular pH. (a) Schematic diagram showing randomisation of histidine locations (green circles in the shaded protein shape), with all proteins in the dataset sampled 100 times in this scheme. Background negative (red) and positive (blue) charges are not moved. (b) Correlations (given as R2) sampled over the 100 randomisations and compared with the actual value (R2 = 0.92). These correlations are between subcellular pH and computed average ΔpKa per histidine (in each subcellular compartment), where the ΔpKa calculations follow the simplified scheme described in Methods.