Protein-encapsulated bilirubin: paving the way to a useful probe for singlet oxygen. Issue 4 (2nd January 2015)

• Record Type: Journal Article
• Authors: Pimenta, Frederico M.; Jensen, Jan K.; Etzerodt, Michael; Ogilby, Peter R.
• Is Part Of: Photochemical & photobiological sciences. Volume 14:Issue 4(2015:Apr.)
• Page Start: 665
• Page End: 677
• Publication Date: 2015-01-02
• Subjects: Photochemistry -- Periodicals; Photobiology -- Periodicals; 541.35
• DOI: 10.1039/c4pp00408f
• Languages: English
• ISSNs: 1474-905X

Abstract

Abstract : Oxygen- and singlet-oxygen-dependent parameters that characterize the behavior of bilirubin encapsulated in a protein have been quantified. Abstract : When dissolved in a bulk solvent, bilirubin efficiently removes singlet molecular oxygen, O2 (a 1 Δ g ), through a combination of chemical reactions and by promoting the O2 (a 1 Δg )→O2 (X 3 Σg − ) nonradiative transition to populate the ground state of oxygen. To elucidate how such processes can be exploited in the development of a biologically useful fluorescent probe for O2 (a 1 Δg ), pertinent photophysical and photochemical parameters of bilirubin encapsulated in a protein were determined. The motivation for studying a protein-encapsulated system reflects the ultimate desire to (a) use genetic engineering to localize the probe at a specific location in a living cell, and (b) provide a controlled environment around the chromophore/fluorophore. Surprisingly, explicit values of oxygen- and O2 (a 1 Δg )-dependent parameters that characterize the behavior of a given chromophore/fluorophore encased in a protein are not generally available. To the end of quantifying the effects of such an encasing protein, a recently discovered bilirubin-binding protein isolated from a Japanese eel was used. The data show that this system indeed preferentially responds to O2 (a 1 Δg ) and not to the superoxide ion. However, this protein not only shields bilirubin such that the rate constants for interaction with O2 (a 1 Δg ) decrease relative to what is observed in a bulk solvent, but the fraction of the total O2 (a 1 Δg )–bilirubin interaction that results in a chemical reaction between O2 (a 1 Δg ) and bilirubin also decreases appreciably. The rate constants thus obtained provide a useful starting point for the general design and development of reactive protein-encased fluorescent probes for O2 (a 1 Δg ).