Monday, 23 May 2005

This presentation is part of: Biological Chemistry Posters

Electrostatic interaction between supramolecular host-guest assembly and zinc-substituted cytochrome c

Cynthia Pagba1, Jane M. Vanderkooi2, Kurt Deshayes3, Eugene Piatnitski4, and Piotr Piotrowiak1. (1) Rutgers University at Newark, Newark, NJ, (2) University of Pennsylvania, Philadelphia, PA, (3) Genentech Incorporated, South San Francisco, CA, (4) Imclone Systems

The binding of supramolceular host-guest assembly to zinc-substituted cytochrome c is investigated by monitoring the electron transfer quenching of the long-lived triplet phosphorescence of the protein by selected metallocenes (namely; ferrocene, ruthenocene and nickelocene) encapsulated in a water-soluble octacarboxyhemicarcerand. The association between cytochrome c and hemicarcerand is evident in the observed spectral shifts exhibited by the protein in the presence of the empty cage. Both the emission and absorption spectra of the protein with the empty hemicarcerand are slightly blue-shifted. Moreover, enhanced phosphorescence intensity is obtained for protein with the empty cage. Introduction of metallocene into the cage, however, significantly reduces the emission intensity with corresponding decrease in the observed lifetimes of the protein. The quenching rates obtained vary with the pH of the medium, which is indicative of the electrostatic nature of the protein-cage interaction. As expected, the degree of phosphorescence quenching also depends on the metallocene used suggesting the role of their different redox potentials. These observed quenching rates are used to estimate the protein-hemicarcerand binding constants and to deduce the approximate binding site.

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