TABLE 1:
Properties of cyan fluorescent proteins and long Stokes shift red fluorescent proteins.
| One-photon property | Two- photon property | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Fluorescent protein | Emission maximum (nm) | Quantum yield (QY) | Excitation maximum (nm) | Extinction coefficient ε(M−1 cm−1) | One-photon brightness, QY × ε × 10−3 | Two-photon excitation maximum (nm) | Two-photon cross section, σ2P (GM) | Two- photon brightness, σ2P (GM) × QY | Photostability half-time (s) | pKa | Maturation half-time (h) |
| ECFP (Ai et al., 2006) | 475 | 0.52a | 433 | 33,000 | 13.5 | 857 | 23a | 12a | 64 | 4.7 | n.d. |
| Cerulean (Rizzo et al., 2004) | 475 | 0.58a | 433 | 43,000 | 27.5 | 858 | 23a | 13a | 36 | 4.7 | n.d. |
| mTFP1 (Ai et al., 2006) | 492 | 0.84a | 462 | 64,000 | 54.4 | 875 | 70a | 59a | 163 | 4.3 | n.d. |
| mTurquoise2 (Goedhart et al., 2012) | 474 | 0.93 | 434 | 30,000 | 27.9 | 860 | 30 | 28a | 256 | 3.1 | n.d. |
| hmKeima (this study) | 618 | 0.21 ± 0.03 | 430 | 34,100 | 7.2 | 870 | 73 | 15 | n.d. | 5.97 | 4.0 |
| hmKeima4.15 (this study) | 612 | 0.29 ± 0.04 | 436 | 28,000 | 8.1 | 870 | 60 | 17 | n.d. | 5.18 | 3.8 |
| hmKeima8.5 (this study) | 612 | 0.34 ± 0.05 | 438 | 32,000 | 10.9 | 870 | 65 | 22 | n.d. | 5.31 | 3.8 |
Four cyan fluorescent proteins (ECFP, Cerulean, mTFP1, and mTurquoise) and three long Stokes shift red proteins (hmKeima, hmKeima4.15, and hmKeima8.5) are compared with regard to various single- and two-photon properties.