Ernesto M. Arbeloa

UVB Photoprotective Role of Mycosporines in Yeast: Photostability and Antioxidant Activity of Mycosporine-Glutaminol-Glucoside

Abstract Several yeast species are able to synthesize and accumulate UV-radiation-absorbing mycosporine metabolites that are of unclear physiological function. In this work we analyzed the relationship between mycosporine-glutaminol glucoside (MGG) production, cell survival after UVB irradiation, and formation of cyclobutane pyrimidine dimers (CPDs). We also assessed the photostability and singlet oxygen quenching activity of MGG. A set of nine isolates of the basidiomycetous yeast Cryptococcus steppossus cultured in both dark and light conditions was used for the studies. Survival of the UVB-irradiated isolates and MGG concentration had a linear relationship when the concentration was over 2.5 mg g−1. CPD accumulation and MGG accumulation were inversely related. MGG in aqueous solution was photostable with a photodecomposition quantum yield of 1.16 × 10−5. MGG quenching of singlet oxygen was also observed, and the rate constant for the process in D2O was 5.9 × 107 M−1 s−1. Our results support the idea that MGG plays an important role as a UVB photoprotective metabolite in yeasts by protecting against direct damage on DNA and probably against indirect damage by singlet oxygen quenching.

Mycosporine-like amino acid content in the sea anemones Aulactinia marplatensis, Oulactis muscosa and Anthothoe chilensis

The occurrence of mycosporine-like amino acids (MAAs) in the sea anemones Aulactinia marplatensis (Zamponi, 1977), Oulactis muscosa (Drayton in Dana, 1846) and Anthothoe chilensis (Lesson, 1830), from the rocky intertidal habitats on the coast of Mar del Plata, Argentina, was assessed by HPLC. The pattern of MAAs in the mussel Brachidontes rodriguezi, main component of the diet for A. marplatensis and O. muscosa, was as well determined. The results were comparatively analyzed together and with previously reported MAA content in species mainly of the genus Anthopleura. The correlation between the MAA concentration and light availability of their habitats is in line with the photoprotective role assigned to the compounds. The high proportion of mycosporine-taurine in the three species and the results for the evaluation of MAAs in the mussels point to a non-dietary origin or a regulated biotransformation metabolism of dietary MAAs and/or their precursors that is common to sea anemones.

A Comparative Study on the Photophysics and Photochemistry of Xanthene Dyes in the Presence of Polyamidoamine (PAMAM) Dendrimers

The photophysical and photochemical properties of the xanthene dyes Eosin Y, Erythrosin B, and Rose Bengal are evaluated in the presence of amino-terminated polyamidoamine (PAMAM) dendrimers of relatively high generation (G3-G5) in alkaline aqueous solution. UV/Vis absorption and fluorescence spectra of the dyes show bathochromic shifts, which correlate with the size of the dendrimer. Binding constants (Kbind ) are calculated from absorption data. The resulting high Kbind values indicate strong interactions between both molecules. Triplet-triplet absorption spectra of the dyes are recorded by laser flash photolysis, and a decrease in the triplet lifetimes is observed in the presence of dendrimers. At the same time, an increase in the absorption of the semireduced form of the dyes is observed. Rate constants for triplet quenching (3 kq ) and radical quantum yields (ΦR ) are obtained. The results are explained by a very efficient electron-transfer process from PAMAM to xanthene dyes for all of the dye/dendrimer couples that are evaluated.

A Comparative Study on the Photophysical and Photochemical Properties of Dyes in the Presence of Low Generation Amino-terminated PAMAM Dendrimers

The photophysical and photochemical properties of the xanthene dyes mercurochrome (MCr) and eosin‐Y (Eos); and the phenazine dye safranine‐O (SF) are evaluated in the presence of amino‐terminated polyamidoamine (PAMAM) dendrimers of low generations. The dendrimers produce a red shift in the UV‐vis absorption spectra of the dyes, which increases with concentration and the size of the PAMAM molecule. The Stern–Volmer plots of fluorescence quenching for xanthenic dyes present a downward curvature. It is ascribed to a static mechanism involving a dye–dendrimer binding. A non‐linear fitting of the SV plots allows the calculation of the binding constants. For SF, the fluorescence is only slightly quenched by PAMAMs and the SV plots are linear. The binding constants are in the order Kbind (SF) ≪ Kbind (Eos) < Kbind (MCr). The difference must be due to important specific structural effects. A decrease in the triplet lifetime and an increase in the absorption of the semireduced form of the dyes are observed in the presence of dendrimers. While for the two xanthene dyes, the rate constants reach the diffusional limit for G2 and G3, for SF they are one order of magnitude lower. This is explained by a different quenching mechanism of the two types of dyes.