Homo-association de l'hypéricine dans l'eau et conséquences sur ses propriétés photodynamiques

Burel, Laure; Jardon, Pierre

doi:10.1051/jcp/1996930300

Cited by 21 publications

(11 citation statements)

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“…Consequently, another process must also exist, along with the formation of aggregates, which leads to the effective quenching of Hyp fluorescence. The self‐quenching of Hyp fluorescence, when the local concentration of Hyp is high, proposed by Burel and Jardon (67) seems to be a realistic explanation of the observed experimental results.…”

Section: Discussionsupporting

confidence: 60%

Fluorescence Spectroscopic Study of Hypericin‐photosensitized Oxidation of Low‐density Lipoproteins

Kaščáková

Réfrégiers

Jancura

et al. 2005

Photochem & Photobiology

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By means of UV-VIS absorption and fluorescence spectroscopy, we demonstrate that the photosensitizer hypericin (Hyp) interacts nonspecifically with low-density lipoproteins (LDL), most probably with the lipid fraction of LDL. The molar ratio of monomeric Hyp binding to nonoxidized LDL and mildly oxidized LDL is 30:1. Increasing the Hyp concentration further leads to the formation of Hyp aggregates inside the LDL molecule. We also demonstrate that photoactivated Hyp oxidizes LDL in a light dose and excitation wavelength dependent manner. The level of oxidation of LDL depends on the amount of Hyp inside the LDL molecule. The maximum of the photosensitized oxidation of the LDL by Hyp is achieved for a 30:1 molar ratio, which corresponds to the maximum concentration of monomeric form of Hyp in LDL.

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Section: Discussionsupporting

confidence: 60%

Fluorescence Spectroscopic Study of Hypericin‐photosensitized Oxidation of Low‐density Lipoproteins

Kaščáková

Réfrégiers

Jancura

et al. 2005

Photochem & Photobiology

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“…Hypericin in aqueous physiological solution is aggregated (6 I), and binding with albumin helps to solubilize it in monomeric form, which is believed to be important for virucidal action (62). Burel and Jardon have also noted that the photodynamic properties of hypericin are greatly diminished when it is aggregated (63).…”

Section: Introductionmentioning

confidence: 99%

Photophysics of Hypericin and Hypocrellin A in Complex with Subcellular Components: Interactions with Human Serum Albumin

Das¹,

Smirnov²,

Wen³

et al. 1999

Photchem. Photbio.

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Time-resolved fluorescence and absorption measurements are performed on hypericin complexed with human serum albumin, HSA (1:4, 1:1 and approximately 5:1 hypericin: HSA complexes). Detailed comparisons with hypocrellin A/HSA complexes (1:4 and 1:1) are made. Our results are consistent with the conclusions of previous studies indicating that hypericin binds to HSA by means of a specific hydrogen-bonded interaction between its carbonyl oxygen and the N1-H of the tryptophan residue in the IIA subdomain of HSA. (They also indicate that some hypericin binds nonspecifically to the surface of the protein.) A single-exponential rotational diffusion time of 31 ns is measured for hypericin bound to HSA, indicating that it is very rigidly held. Energy transfer from the tryptophan residue of HSA to hypericin is very efficient and is characterized by a critical distance of 94 A, from which we estimate a time constant for energy transfer of approximately 3 x 10(-15) s. Although it is tightly bound to HSA, hypericin is still capable of executing excited-state intramolecular proton (or hydrogen atom) transfer in the approximately 5:1 complex, albeit to a lesser extent than when it is free in solution. It appears that the proton transfer process is completely impeded in the 1:1 complex. The implications of these results for hypericin (and hypocrellin A) are discussed in terms of the mechanism of intramolecular excited-state proton transfer, the mode of binding to HSA and the light-induced antiviral and antitumor activity.

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“…Hypericin in aqueous physiological solution is aggregated (125,128), and binding with albumin helps to solubilize it in monomeric form, which is believed to be important for virucidal action. For example, Burel and Jardon have noted that the photodynamic properties of hypericin are greatly diminished when it is aggregated (129).…”

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confidence: 99%

Photophysics and Multifunctionality of Hypericin‐Like Pigments in Heterotrich Ciliates: A Phylogenetic Perspective

Lobban

Hallam

Mukherjee

et al. 2007

Photochem & Photobiology

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In this paper, we review the literature and present some new data to examine the occurrence and photophysics of the diverse hypericin-like chromophores in heterotrichs, the photoresponses of the cells, the various roles of the pigments and the taxa that might be studied to advance our understanding of these pigments. Hypericin-like chromophores are known chemically and spectrally so far only from the stentorids and Fabrea, the latter now seen to be sister to stentorids in the phylogenetic tree. For three hypericin-like pigments, the structures are known but these probably do not account for all the colors seen in stentorids. At least eight physiological groups of Stentor exist depending on pigment color and presence ⁄ absence of zoochlorellae, and some species can be bleached, leading to many opportunities for comparison of pigment chemistry and cell behavior. Several different responses to light are exhibited among heterotrichs, sometimes by the same cell; in particular, cells with algal symbionts are photophilic in contrast to the well-studied sciaphilous (shadeloving) species. Hypericin-like pigments are involved in some well-known photophobic reactions but other pigments (rhodopsin and flavins) are also involved in photoresponses in heterotrichs and other protists. The best characterized role of hypericin-like pigments in heterotrichs is in photoresponses and they have at least twice evolved a role as photoreceptors. However, hypericin and hypericin-like pigments in diverse organisms more commonly serve as predator defense and the pigments are multifunctional in heterotrichs. A direct role for the pigments in UV protection is possible but evidence is equivocal. New observations are presented on a folliculinid from deep water, including physical characterization of its hypericin-like pigment and its phylogenetic position based on SSU rRNA sequences. The photophysics of hypericin and hypericin-like pigments is reviewed. Particular attention is given to how their excited-state properties are modified by the environment. Dramatic changes in excited-state behavior are observed as hypericin is moved from the homogeneous environment of organic solvents to the much more structured surroundings provided by the complexes it forms with proteins. Among these complexes, it is useful to consider the differences between environments where hypericin is not found naturally and those where it is, notably, for example, in heterotrichs. It is clear that interaction with a protein modifies the photophysics of hypericin and understanding the molecular basis of this interaction is one of the outstanding problems in elucidating the function of hypericin and hypericin-like chromophores.

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Homo-association de l'hypéricine dans l'eau et conséquences sur ses propriétés photodynamiques

Cited by 21 publications

References 0 publications

Fluorescence Spectroscopic Study of Hypericin‐photosensitized Oxidation of Low‐density Lipoproteins

Fluorescence Spectroscopic Study of Hypericin‐photosensitized Oxidation of Low‐density Lipoproteins

Photophysics of Hypericin and Hypocrellin A in Complex with Subcellular Components: Interactions with Human Serum Albumin

Photophysics and Multifunctionality of Hypericin‐Like Pigments in Heterotrich Ciliates: A Phylogenetic Perspective

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