注意：GFP的不一定

GFP虽然可以荧光，但是其激发、发射波长却不一定。主要是因为一些突变，造成的波长移动。

Wild type GFP from jellyfish has two excitation peaks, a major one at 395 nm and a minor one at 475 nm with extinction coefficient of 30,000 and 7,000 M-1 cm-1, respectively. Its emission peak is at 509 nm in the lower green portion of the visible spectrum. The GFP from the sea pansy exhibits a single major excitation peak at 498 nm. Crystals of GFP exhibits a nearly identical fluorescence spectrum and lifetime to that for GFP in aqueous solution.

For wild type GFP, exciting the protein at 395 nm leads to rapid quenching of the fluorescence with an increase in the 475 nm excitation band. This photoisomerization effect is prominent with irradiation of GFP by UV light. In a wide range of pH, increasing pH leads to a reduction in fluorescence by 395 nm excitation and an increased sensitivity to 475 nm excitation.

Some mutants of the GFP gene have been produced which have increased fluorescence. The major excitation peak has been red-shifted to 490 nm with the emission staying at 509 nm. This is better for use with standard optical filter sets, as the mutant GFPs have excitation range more compatible with the commonly available optical filters. This also is more useful for confocal laser scanning applications. The corrected excitation and emission spectra of GFP and some of its variants (termed as BlueFP, CyanFP, GreenFP and YellowFP variants) are shown here: