Question

Neutral lysine can be written HL. The other forms of lysine are${\mathbf{H}}_{\mathbf{3}}{\mathbf{L}}^{\mathbf{2}\mathbf{+}}\mathbf{,}{\mathbf{H}}_{\mathbf{2}}{\mathbf{L}}^{\mathbf{+}}\mathbf{,}$and${\mathbf{L}}^{\mathbf{-}}$. The isoelectric point is the pH at which the average charge of lysine is $\mathbf{0}$. Therefore, at the isoelectric point,$\mathbf{2}\left[H_3{L}^{2+}\right]\mathbf{+}\left[H_2{L}^{+}\right]\mathbf{=}\left[L^{-}\right]$. Use this condition to calculate the isoelectric pH of lysine.

Short answer

The isoelectric pH of lysine as found to be $9.95$

Step-by-step solution

Definition of isoelectric pH.

The isoelectric point is the pH at which a molecule has no net electrical charge or is electrically neutral. pH is the conventional abbreviation for the isoelectric point.

The pH of lysine.

The fraction of lysine in the form of${\mathrm{H}}_3{\mathrm{L}}^{2-}$is negligible so the expression of electro neutrality technique reduced to$\left[{\mathrm{H}}_2{\mathrm{L}}^{+}\right]=\left[{\mathrm{L}}^{-}\right]{\mathrm{H}}_3{\mathrm{L}}^{2-}$. Hence the isoelectric

$$\begin{gathered} \mathrm{pH}=\frac{1}{2}\left({\mathrm{pK}}_2+{\mathrm{pK}}_3\right) \\ =9.95 \end{gathered}$$