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Preparation and characterization of pentaammineruthenium-(histidine-83)azurin: Thermodynamics of intramolecular electron transfer from ruthenium to copper

Margalit, Ruth and Kostic, Nenad M. and Che, Chi-Ming and Blair, David F. and Chiang, Huey-Jenn and Pecht, Israel and Shelton, Joan B. and Shelton, J. Roger and Schroeder, Walter A. and Gray, Harry B. (1984) Preparation and characterization of pentaammineruthenium-(histidine-83)azurin: Thermodynamics of intramolecular electron transfer from ruthenium to copper. Proceedings of the National Academy of Sciences of the United States of America, 81 (20). pp. 6554-6558. ISSN 0027-8424. http://resolver.caltech.edu/CaltechAUTHORS:MARpnas84

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Abstract

The reaction between a5RuH2O2+ (a is NH3) and Pseudomonas aeruginosa azurin at pH 7, followed by oxidation, yields a5Ru(His-83)3+-azurin(Cu2+) as the major product. Spectroscopic measurements (UV-visible, CD, EPR, and resonance Raman) indicate that the native structure is maintained in the modified protein. The site of ruthenium binding (His-83) was identified by peptide mapping. The a5RuHis/Cu ratio in the modified protein, determined from the EPR spectrum, is 1:1, and the reduction potentials (vs. normal hydrogen electrode, pH 7.0, 25 degrees C) are blue copper (Cu2+/1+), 320 ± 2 mV; a5Ru(His-83)3+/2+, 50 ± 10 mV. From measurements of the reduction potentials at several temperatures in the 5-40 degrees C range, delta-H degrees for intramolecular Ru2+ --> Cu2+ electron transfer was estimated to be -12.4 kcal mol(-1) (1 cal = 4.184 J). Analysis of kinetic data in light of the electron transfer exothermicity indicates that the reorganizational enthalpy of the blue copper site can be no larger than 7.1 kcal mol(-1).


Item Type:Article
Additional Information:Copyright © 1984 by the National Academy of Sciences. Contributed by Harry B. Gray, May 29, 1984. We thank Stephen Mayo for Fig. 3, Vance Morgan for help with the CD measurements, Tin Wu Tang for assistance with cyclic voltammetry, and Ting Lin Kao for a sample of Na[Co(EDTA)]. Helpful comments were provided by Walther Ellis, Karl Freed, Michel Goldberg, Brian Hoffman, John Hopfield, Noel Hush, Sven Larsson, George McLendon, Bo Malmstrom, and Rudy Marcus. This research was supported by National Institutes of Health Grants AM19038 (H.B.G.) and HL02558 (W.A.S.). This is contribution no. 7033 from the Arthur Amos Noyes Laboratory. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Subject Keywords:ruthenium-histidine binding, protein modification, blue copper, oxido-reduction, reorganization energy
Record Number:CaltechAUTHORS:MARpnas84
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:MARpnas84
Alternative URL:http://www.pnas.org/cgi/content/abstract/81/20/6554
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:955
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:15 Nov 2005
Last Modified:26 Dec 2012 08:42

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