Table 4.
pH sensitivity (pKa) of selected fluorescent protein variants.
| Fluorescent Protein | pKa | Notes | Reference |
|---|---|---|---|
| Blue | |||
| mTagBFP2 | 2.7 | [116] | |
| Cyan | as a class, cyan FPs are relatively pH insensitive | ||
| ECFP, mCerulean | 4.7 | [133] | |
| mTFP1 | 4.3 | [134] | |
| mCerulean3 | 3.2 | [135] | |
| mTurquoise2 | 3.1 | [118] | |
| Green | as a class, green FPs are moderately pH sensitive | ||
| mEGFP, mEmerald | 6.0 | [136] | |
| mNeonGreen | 5.7 | [122] | |
| mTagGFP2 | 5.0 | [123] | |
| T-Sapphire | 4.9 | a UV-excited green FP | |
| superecliptic pHluorin | 7.2 | purposely optimized to be very pH sensitive | [137] |
| Yellow | as a class, modern yellow FPs are moderately pH sensitive | ||
| EYFP | 6.9 | very pH sensitive, newer variants are somewhat improved | |
| mVenus, SYFP2 | 6.0 | [117,138] | |
| mCitrine | 5.7 | [136] | |
| Orange | |||
| mKO2 | 5.0–5.5 | [125] | |
| mOrange, mOrange2 | 6.5–7.5 | very pH sensitive | [125] |
| Red | as a class, red FPs are relatively pH insensitive | ||
| mRFP1, mCherry, mStrawberry | ≤4.5 | [9] | |
| TagRFP-T | 4.0 | [125] | |
| FusionRed | 4.6 | [127] | |
| Far-Red | |||
| mKate2 | 5.4 | [126] | |
| mNeptune | 5.8 | [128] |