Negatively charged (acidic)
Glutamate
Glu · E · 147.13 Da
Charged
Non-essential
Carboxylate (-COO⁻)
The principal excitatory neurotransmitter in the central nervous system.
Ionization ladder
| pKa | Group | Change | Charge |
|---|---|---|---|
| 2.19 | α-carboxyl | -COOH → -COO⁻ | 0 → −1 |
| 4.25 | side chain | neutral → deprotonated | 0 → −1 |
| 9.67 | α-amino | -NH₃⁺ → -NH₂ | +1 → 0 |
pI = (2.19 + 4.25) / 2 = 3.22, the midpoint of the two pKa values that bracket the neutral species.
Net charge across pH
pH 1+1
pH 40
pH 7−1
pH 10−2
pH 13−2
A group is deprotonated once the pH climbs past its pKa. Add the contributions and you have the net charge, with no memorization required.