FIG. 2.

(a) Comparison of the numerically calculated and analytically determined threshold charge, $Q_{\text{t}}$ corresponding to ${\eta }_{\text{t}}=0.95$ at which the onset of charge regulation occurs in a spherical charge distribution of radius, R, with ${\varphi }_{\text{s}}=0$. Symbols denote calculations and lines denote the result of Eq. (5). Color denotes different salt concentrations: $\sim 100$ mM (black) and $\sim 1$ mM (green). Open symbols and dashed lines denote R = 5.1 nm, while closed symbols and solid lines represent R = 2.55 nm. (b) Histogram of $Q/R_{\text{g}}$ values for $\sim \mathrm{11\hspace{0.17em}000}$ globular monomeric proteins, where $R_{\text{g}}$ denotes the calculated radius of gyration of each molecule based on its atomic structure.