Phenothiazine dyes photosensitize protein damage through electron transfer and singlet oxygen generation

- We examined the mechanism of photosensitized protein damage by phenothiazine dyes.
- Methylene blue and its analogues photosensitized damage of tryptophan residue of human serum albumin.
- Scavenger effect on the photosensitized protein damage supports the contribution of singlet oxygen mechanism.
- Contribution of electron transfer-mediated mechanism was also suggested.
- The quantum yields of these mechanisms could be determined.

Photosensitized protein damage is an important process in medical applications of photochemical reaction, such as photodynamic therapy. A similar method has been applied to photodynamic antimicrobial chemotherapy (PACT), which can treat sinusitis and periodontal disease. For example, methylene blue is used as a photosensitizer for PACT. However, the mechanism of PACT has not been clarified completely. In this study, protein damage photosensitized by methylene blue and its analogues was examined. The scavenger effect on protein photodamage by dyes and fluorescence measurements suggests the contribution of the electron transfer mechanism to this photosensitized protein damage as the singlet oxygen generation mechanism. The quantum yields of protein damage by these photosensitizers could be determined. The electron transfer mechanism is the direct electron abstraction from the biomolecule to the photoexcited photosensitizer. Because this mechanism does not necessarily require oxygen in vivo, the mechanism of PACT, such as in sinusitis treatment by methylene blue under a hypoxic condition, might be explained by the electron transfer.

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