Campus Units

Chemistry

Document Type

Article

Publication Version

Published Version

Publication Date

9-27-2005

Journal or Book Title

Journal of Physical Chemistry B

Volume

109

Issue

41

First Page

19484

Last Page

19489

DOI

10.1021/jp051645u

Abstract

The photophysics of hypericin have been studied in its complex with two different isoforms, A1-1 and P1-1, of the protein glutathione S-transferase (GST). One molecule of hypericin binds to each of the two GST subunits. Comparisons are made with our previous results for the hypericin/human serum albumin complex (Photochem. Photobiol. 1999, 69, 633−645). Hypericin binds with high affinity to the GSTs:  0.65 μM for the A1-1 isoform and 0.51 μM for the P1-1 isoform (Biochemistry 2004, 43, 12761−12769). The photophysics and activity of hypericin are strongly modulated by the binding protein. Intramolecular hydrogen-atom transfer is suppressed in both cases. Most importantly, while there is significant singlet oxygen generation from hypericin bound to GST A1-1, binding to GST P1-1 suppresses singlet oxygen generation to almost negligible levels. The data are rationalized in terms of a simple model in which the hypericin photophysics depends entirely upon the decay of the triplet state by two competing processes, quenching by oxygen to yield singlet oxygen and ionization, the latter of these two are proposed to be modulated by A1-1 and P1-1.

Comments

Reprinted (adatped) with permission from Journal of Physical Chemistry B 109 (2005): 19484, doi: 10.1021/jp051645u. Copyright 2005 American Chemical Society.

Copyright Owner

American Chemical Society

Language

en

File Format

application/pdf

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