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1 August 2001 Spectroscopic Study of Visible-light Effects on Hypericin-lens Proteins Systems
Antonella Sgarbossa, Francesco Lenci
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Molecular interactions between hypericin and α-, β- and γ-crystallin proteins have been studied by means of absorption and steady-state fluorescence spectroscopy, aiming to clarify if and how the pigment binds to the proteins and to investigate the effects of visible-light irradiation on these molecular systems. Such a study is a prerequisite for assessing the possibility of using hypericin as a mild antidepressant and/or as a photodynamic agent for the treatment of eye tumors and eye viral and bacterial diseases without side injuries to the lens. We have shown that in dark-kept samples, with increasing α-crystallin concentration, both the fluorescence emission intensity and the ratio of the absorption maxima around 590 and 550 nm of hypericin increase. These effects have been attributed to the monomerization of nonfluorescent hypericin aggregates caused by the binding of the pigment to α-crystallin. The binding constant of hypericin has been evaluated to be of the order of 3.0 (mg/mL)−1, corresponding to a dissociation constant of the order of 0.3 mg/mL. Following irradiation with light of wavelengths over 400 nm, at an irradiance of 20 mW/cm2, both tryptophan and hypericin fluorescence emission intensities decrease. These effects are suggested to be the consequence of a spatial rearrangement of the protein framework which takes place following the α-crystallin photopolymerization sensitized by hypericin itself described in the literature. For the sake of comparison hypericin has been studied also in the presence of βH-, βL- and γ-crystallins at the same concentration.

Antonella Sgarbossa and Francesco Lenci "Spectroscopic Study of Visible-light Effects on Hypericin-lens Proteins Systems," Photochemistry and Photobiology 74(2), 196-200, (1 August 2001).<0196:SSOVLE>2.0.CO;2
Received: 22 January 2001; Accepted: 1 May 2001; Published: 1 August 2001

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