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nmdcat.online June 29, 2026

The isoelectric point (pI) of an amino acid is defined as the pH at which

A. The amino acid is fully protonated and carries a net positive charge
B. The amino acid has no net electrical charge and does not migrate in an electric field
✓
C. The solubility of the amino acid in water is at its maximum
D. The amino acid exclusively exists in the D-configuration

📝 Explanation

The pI is the pH where the net charge on the amino acid is zero. At this pH, the molecule is a zwitterion and will not move towards either the anode or cathode during electrophoresis. For neutral amino acids, pI is the average of pKₐ₁ and pKₐ₂.

📖 Additional Information

  • The amino acid is fully protonated and carries a net positive charge
  • The amino acid has no net electrical charge and does not migrate in an electric field
  • The solubility of the amino acid in water is at its maximum
  • The amino acid exclusively exists in the D-configuration

The pI is the pH where the net charge on the amino acid is zero. At this pH, the molecule is a zwitterion and will not move towards either the anode or cathode during electrophoresis. For neutral amino acids, pI is the average of pKₐ₁ and pKₐ₂.

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