Photosensitization activity of normal and Hyperporphyirins self-assembled with recombinant albumin: Consequences for the development of engineered photoreceptor proteins.

This study investigates how metal coordination and protein binding modulate the photosensitizing properties of protoporphyrin IX (PpIX) analogues and their potential for creating engineered photoreceptor proteins (EPrP). Three porphyrins-metal-free PpIX (mfPpIX, normal), hemin (d-type hyperporphyrin), and tin-PpIX (SnPpIX, p-type hyperporphyrin)-were self-assembled with recombinant human serum albumin (rHSA) and irradiated at their Soret band using a 405 nm laser. Steady-state and time-resolved spectroscopic analyses revealed distinct photophysical behaviors. mfPpIX strongly binds rHSA and exhibits efficient photosensitization of singlet oxygen (1O2), leading to photobleaching and formation of formyl-type photoproducts, suggesting ROS-mediated mechanisms as potential triggers for EPrP. Hemin showed negligible photosensitization, dominated by intramolecular charge transfer to Fe, limiting its suitability for ROS-driven EPrP. SnPpIX retained significant 1O2 photosensitization and photoproduct formation both free and protein-bound, but its weak interaction with rHSA may constrain its applicability. These findings highlight mfPpIX as the most promising candidate for EPrP development and provide novel quantitative data on absorption, fluorescence, and lifetime properties of aqueous porphyrins, including the first reported parameters for SnPpIX and PpIX photoproducts, besides the identification of the contribution of aqueous monomeric PpIX to the emission properties.