The pI of glutamic acid is equal to the average pK_a of its two negatively charged carboxyl groups. Explain.

• A. In order for glutamic acid to have no net charge, the two carboxyl groups must have a charge of −1 between them in order to cancel out the +1 charge of the amino group.
• B. In order for glutamic acid to have no net charge, the two carboxyl groups must have a charge of +1 between them in order to cancel out the −1 charge of the amino group.
• C. In order for glutamic acid to have no net charge, the two amino groups must have a charge of −1 between them in order to cancel out the +1 charge of the carboxyl group.
• D. In order for glutamic acid to have no net charge, the two amino groups must have a charge of +1 between them in order to cancel out the −1 charge of the carboxyl group.

Answer: (A)