Give the pKa values for the protonatable groups of glutamate, and then calculate

Question

Give the pKa values for the protonatable groups of glutamate, and then calculate its pl (Answers within ± 0.3 pH units will be accepted) Number Number (-NH3') CH2 -CoOH) CH2 Number Number The pl of glutamate OH R group COOH) O Previous Give Up & View Solution 0 Check Answer Next Hint The structure is shown in its fully protonated form. Regular organic acids, RCOOH, have pKa values of about 4.8. Regular organic amines, RNH3, have pKa values of about 10.5. Consider how the neighboring functional groups in the molecule will affect each pKa value

Explanation / Answer

pKa (NH3+) = 9.67

pKa (COOH) = 2.19

pKa (R group COOH) = 4.25

The pI or isoelectric point of glutamate is its pH when it is neutral. In its neutral state, NH3+ is not protonated so the pKa of only the two COOH groups are relevant. The pI is obtained by averaging these two pKa values.

pI = pKa (COOH) + pKa (R group COOH) / 2 = (2.19+ 4.25)/2 = 3.22

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