The binding of analogs of porphyrins and chlorins with elongated side chains to albumin

Shimshon Ben Dror, Irena Bronshtein, Hana Weitman, Kevin M. Smith, William G. O'Neal, Peter A. Jacobi, Benjamin Ehrenberg

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17 Scopus citations


In previous studies, we demonstrated that elongation of side chains of several sensitizers endowed them with higher affinity for artificial and natural membranes and caused their deeper localization in membranes. In the present study, we employed eight hematoporphyrin and protoporphyrin analogs and four groups containing three chlorin analogs each, all synthesized with variable numbers of methylenes in their alkyl carboxylic chains. We show that these tetrapyrroles' affinity for bovine serum albumin (BSA) and their localization in the binding site are also modulated by chain lengths. The binding constants of the hematoporphyrins and protoporphyrins to BSA increased as the number of methylenes was increased. The binding of the chlorins depended on the substitution at the meso position opposite to the chains. The quenching of the sensitizers' florescence by external iodide ions decreased as the side chains became longer, indicating to deeper insertion of the molecules into the BSA binding pocket. To corroborate this conclusion, we studied the efficiency of photodamage caused to tryptophan in BSA upon illumination of the bound sensitizers. The efficiency was found to depend on the side-chain lengths of the photosensitizer. We conclude that the protein site that hosts these sensitizers accommodates different analogs at positions that differ slightly from each other. These differences are manifested in the ease of access of iodide from the external aqueous phase, and in the proximity of the photosensitizers to the tryptophan. In the course of this study, we developed the kinetic equations that have to be employed when the sensitizer itself is being destroyed.

Original languageEnglish
Pages (from-to)847-855
Number of pages9
JournalEuropean Biophysics Journal
Issue number7
StatePublished - Sep 2009

Bibliographical note

Funding Information:
Acknowledgments We thank Mr. Hui Wang, who prepared several of the chlorin samples. We acknowledge the support (Grant No. 2002-383) of the United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel (to K. M. S. and B. E.) We also acknowledge the support of the Michael David Falk Chair in Laser Phototherapy (to B. E.). Financial support of this work by the National Institutes of Health, NIGMS Grant No. GM38913 (to P. A. J.) is gratefully acknowledged.


  • Albumin
  • Binding
  • Chlorin
  • Hematoporphyrin
  • Photosensitization
  • Protoporphyrin


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