Consider the following sequence for aspartic acid

The isoelectronic point (PI) of aspartic acid is

At isoelectric point of aspartic acid, we have

$\left[{\text{H}}_{\text{2}}{\text{N}}^{+}{\text{CH(CH}}_{\text{2}}{\text{COOH)CO}}_{\text{2}}\text{H}\right]=\left[{\text{H}}_{\text{3}}{\text{N}}^{+}{\text{CH(CH}}_{\text{2}}{\text{COO}}^{-}){{\text{CO}}_{\text{2}}}^{-}\right]$

Hence, $\text{The\hspace{0.17em}\hspace{0.17em}Isoelectronic\hspace{0.17em}\hspace{0.17em}Point}\left(PI\right)=\frac{1}{2}(\text{p}{K}_1+\text{p}{K}_{\text{R}})$

$=\frac{1}{2}(1.88+3.65)$=2.77.