Abstract: There are two spectral types of R-phycoerythrin (R-PE) in red algae. One is the triple peak type R-PE with absorption maxima at 498, 540 and 565 nm. The other is the double peak type R-PE with absorption maxima at 498 and 565 nm, and an absorption shoulder at 540 nm.The fluorescence spectra and the lifetime of the two types of R-PE at various pH are studied. They are partly denatured at pH 3.6. The fluorescence intensity is reduced, and the lifetime is shortened. The fluorescence peak positions and the lifetime of triple peak type R-PE remain unchanged at pH6-13, but those of double peak type R-PE are various at pH 13. The fluorescence peak positions are shifted, and the lifetimes become longer. This phenomenon shows that there are certain differences in structures between the two types of R-PE.The concentration effects of the fluorescence spectra of R -PE are observed. The fluorescence peak positions are red shifted, the intensities are increased, then decreased, and the lifetimes become longer with the increase of protein concentrations. The fluorescence of R-PE is quenched by iodide ion. Meanwhile, the lifetime of R-PE tends to shortening. Stern-Volmer plot is obtained. The Stern-Volmer lines are not identical with different R -PE because of the different conformations they have.

Key words: R-phycoerythrin, fluorescence spectra, fluorescence lifetime, fluorescence quenching