Question

Do the following compounds migrate to the cathode or to the anode on electrophoresis at the specified \(\mathrm{pH}\) ? (a) Histidine at \(\mathrm{pH} 6.8\) (b) Lysine at \(\mathrm{pH} 6.8\) (c) Glutamic acid at \(\mathrm{pH} \mathrm{} 4.0\) (d) Glutamine at \(\mathrm{pH} \mathrm{} 4.0\) (e) Glu-Ile-Val at pH \(6.0\) (f) Lys-Gln-Tyr at pH \(6.0\)

Short answer

Explain your answer. (a) Histidine at pH 6.8 (b) Lysine at pH 6.8 (c) Glutamic acid at pH 4.0 (d) Glutamine at pH 4.0 (e) Glu-Ile-Val at pH 6.0 (f) Lys-Gln-Tyr at pH 6.0

Step-by-step solution

Find the isoelectric points (pI) of the compounds

Refer to the literature or any available resources to find the pI values for each compound: (a) Histidine (pI = 7.59) (b) Lysine (pI = 9.74) (c) Glutamic acid (pI = 3.22) (d) Glutamine (pI = 5.65) (e) Glu-Ile-Val, a tripeptide of Glutamic acid, Isoleucine, and Valine (pI ≈ 3.22 + 6.02 + 5.96) (f) Lys-Gln-Tyr, a tripeptide of Lysine, Glutamine, and Tyrosine (pI ≈ 9.74 + 5.65 + 5.66)

Compare the pH and pI

Determine if the pH given is less than or greater than the pI for each compound. (a) Histidine at pH 6.8: pH < pI (6.8 < 7.59) (b) Lysine at pH 6.8: pH < pI (6.8 < 9.74) (c) Glutamic acid at pH 4.0: pH > pI (4.0 > 3.22) (d) Glutamine at pH 4.0: pH < pI (4.0 < 5.65) (e) Glu-Ile-Val at pH 6.0: pH ≈ pI (6.0 ≈ 5.07) (f) Lys-Gln-Tyr at pH 6.0: pH < pI (6.0 < 6.68)

Determine the migration direction

Based on the comparison of pH and pI, determine if the compound will migrate to the anode or to the cathode. (a) Histidine at pH 6.8: pH < pI, migrate to the anode (b) Lysine at pH 6.8: pH < pI, migrate to the anode (c) Glutamic acid at pH 4.0: pH > pI, migrate to the cathode (d) Glutamine at pH 4.0: pH < pI, migrate to the anode (e) Glu-Ile-Val at pH 6.0: pH ≈ pI, no significant migration (f) Lys-Gln-Tyr at pH 6.0: pH < pI, migrate to the anode