Phototoxicity of halogenofluorescein derivatives in Dictyostelium discoideum amoebae: comparison of 2′,4′,5′,7′-tetrabromofluorescein- and 4′,5′-diiodofluorescein dextran
The halogenated fluorescein derivatives: 2′,4′,5′,7′-tetrabromofluorescein isothiocyanate dextran (Br4FD) and 4′,5′-diiodofluorescein isothiocyanate dextran (I2FD), were found to be efficient photosensitizers for the production of singlet oxygen. The singlet oxygen quantum yields were determined by reaction with acceptors in aqueous solution. Their comparison showed that the singlet oxygen quantum yield of Br4FD was threefold higher than that of I2FD. Br4FD was more resistant to photobleaching than I2FD. Both derivatives were internalized by fluid-phase pinocytosis in amoebae of the cellular slime mould Dictyostelium discoideum. Subsequently, illumination of cells led to a dose-dependent loss of viability consistent with a role for singlet oxygen generated inside the endosomal compartments in the mechanism of photoinjury. Br4FD showed a three-fold higher efficiency than I2FD for photoinduced cytotoxicity.
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Phototoxicity of halogenofluorescein derivatives in Dictyostelium discoideum amoebae: comparison of 2′,4′,5′,7′-tetrabromofluorescein- and 4′,5′-diiodofluorescein dextran