Polar, uncharged
Threonine
Thr · T · 119.12 Da
EssentialGlucogenic and ketogenicHydroxyl-containing
Essential
Hydroxyl (secondary alcohol)
Like isoleucine, branched at Cβ with two chiral centers. Both a phosphorylation site and an O-glycosylation anchor.
Ionization ladder
| pKa | Group | Change | Charge |
|---|---|---|---|
| 2.11 | α-carboxyl | -COOH → -COO⁻ | 0 → −1 |
| 9.62 | α-amino | -NH₃⁺ → -NH₂ | +1 → 0 |
pI = (2.11 + 9.62) / 2 = 5.86, the midpoint of the two pKa values that bracket the neutral species.
Net charge across pH
pH 1+1
pH 40
pH 70
pH 10−1
pH 13−1
A group is deprotonated once the pH climbs past its pKa. Add the contributions and you have the net charge, with no memorization required.