Table 1.
Spectral characteristics of recombinant pH-probes. The real isosbestic point is derived from normalized spectra whereas the apparent isosbestic point is from the raw data. The Stokes-shifts are defined here by the difference between the wavelength of the major (and the minor) absorption peak and the wavelength of the emission peak. Index 'x' of S designates sensitivity calculated from excitation spectra, and index 'm' values are calculated from emission spectra. 'em', 'ex', and 'abs' designate wavelengths in the emission spectrum, the excitation spectrum, and in the absorption spectrum, respectively.
| GFP-species | |||
| parameter | ratiometric pHluorin | ecliptic pHluorin | Pt-GFP |
| real isosbestic point λiso | 426 nm (ex) | 495 nm (em) | 437 nm (ex) |
| apparent isosbestic point | 428 nm (ex) | 489 nm (em) | 430 nm (ex) |
| left peak WL (λ1 < λiso) | 395 nm (ex, abs) | 464 nm (em) | 390 nm (ex) |
| right peak WL(λ2 > λiso) | 475 nm (ex) | 511 nm (em) | 502 nm (ex) |
| Stokes-shift (λem - λabs) | 113 nm (33 nm) | 114 nm (35 nm) | 6 nm |
| maximum WL (λmax) | 508 nm (em) | 397 nm (ex, abs) | 508 nm (em) |
| Rmax (F(λ1)/F(λ2)) | 2.75 | 14 | 107 |
| Rmin (F(λ1)/F(λ2)) | 0.3 | 0.5 | 4.2 |
| Rmax - Rmin | 2.44 | 13.5 | 103 |
| Rmax/Rmin | 8.7 | 27 | 26 |
| apparent pK (λ1; λ2) | 6.9 | 7.6 | 7.3 |
| Responsiveness (Δlog(R)·ΔpH) | 2.9 | 2.0 | 9.8 |
| pH sensitivity (Sx) | 0.77 | 0.41 | 0.69 |
| pH sensitivity (Sm) | 0.34 | 1.05 | 0.09 |