Steady-state and femtosecond photoinduced processes of blepharismins bound to alpha-crystallin.
The interaction of blepharismin (BP) and oxyblepharismin (OxyBP) with bovine alpha-crystallin (BAC) has been studied both by steady-state and femtosecond spectroscopy, with the aim of assessing the possible phototoxicity of these compounds toward the eye tissues. We showed that these pigments form with BAC potentially harmful ground-state complexes, the dissociation constants of which have been estimated to be 6 +/- 2 micromol L(-1) for OxyBP and 9 +/- 4 micromol L(-1) for BP. Irradiation with steady-state visible light of solutions of blepharismins in the presence of BAC proved to induce a quenching of both the pigment and the intrinsic protein fluorescences. These effects were tentatively rationalized in terms of structural changes of alpha-crystallin. On the other hand, femtosecond transient absorption spectroscopy was used to check the occurrence of any type I photoactivity of oxyblepharismin bound to alpha-crystallin. The existence of a particular type of fast photoinduced reaction, not observed in former studies with human serum albumin but present in the natural oxyblepharismin-binding protein, could here be evidenced but no specific reaction was observed during the first few nanoseconds after excitation. Partial denaturation of alpha-crystallin was however found to alter the excited-state behaviour of its complex with oxyblepharismin, making it partly resemble that of free oxyblepharismin in solution.
Youssef
T
T
National Institute of Laser Enhanced Sciences , Cairo University, Giza, Egypt.
Brazard
J
J
Ley
C
C
Lacombat
F
F
Plaza
P
P
Martin
M M
MM
Sgarbossa
A
A
Checcucci
G
G
Lenci
F
F
D000818:Animals; D002417:Cattle; D004579:Electron Transport; D005123:Eye / Q000187:drug effects / Q000378:metabolism; D008027:Light; D055095:Optics and Photonics; D010569:Perylene / Q000031:analogs & derivatives* / Q000378:metabolism / Q000633:toxicity; D010778:Photochemotherapy; D011485:Protein Binding; D011489:Protein Denaturation; D011522:Protons; D013997:Time Factors; D038201:alpha-Crystallins / Q000378:metabolism*
D011522:Protons; D038201:alpha-Crystallins; C092293:blepharismin; C505951:oxyblepharismin; D010569:Perylene