UVA photoinduced yeast protein modifications by methylene blue and naproxen

Abstract

UVA photosensitization by methylene blue (MB) or by naproxen (NAP) towards cell proteins in yeast Saccharomyces cerevisiae was investigated in order to compare this system with two simpler models, such as free Trp in solution and as a component of bovine and human serum albumin. The process was studied by monitoring protein tryptophan (Trp) residue integrity. The sensitized photodegradation of proteins resulted in different degrees of Trp damage with different Trp (photo)-products. Indeed, many of these Trp derivatives are diagnostic for the photosensitization mechanism and some of them were obtained from cells by UVA photosensitization for the first time in this work. The analysis of quantum yields of photoproduct distribution allowed us to weigh up the type I/II contribution on a UVA photosensitization mechanism. The UVA mediated generation of these Trp derivatives is consistent with the occurrence of singlet oxygen formation (almost dominant in MB), and photoionization (significant in NAP) within the protein matrix. The results obtained in the case of this more complex system (cell) are in agreement with the two simpler models recently studied in our lab. The quantum yields of Trp photoinduced degradation, as well as of its photoproducts formation, decrease with increasing the complexity of the investigated target.