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Electron Transfer in Ruthenium/Zinc Porphyrin Derivatives of Recombinant Human Myoglobins. Analysis of Tunneling Pathways in Myoglobin and Cytochrome c

Casimiro, Danilo R. and Wong, Luet-L. and Colón, Jorge L. and Zewert, Thomas E. and Richards, John H. and Chang, I-Jy and Winkler, Jay R. and Gray, Harry B. (1993) Electron Transfer in Ruthenium/Zinc Porphyrin Derivatives of Recombinant Human Myoglobins. Analysis of Tunneling Pathways in Myoglobin and Cytochrome c. Journal of the American Chemical Society, 115 (4). pp. 1485-1489. ISSN 0002-7863. doi:10.1021/ja00057a037.

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Site-directed mutants of human myoglobin have been prepared and characterized; each protein has a single surface-modifiable histidine (at position 48, 70, or 83). The proteins were modified by covalent attachment of pentaammineruthenium (a_5Ru) to the surface histidine and substitution of zinc mesoporphyrin IX diacid (ZnP) for the heme. Donor-acceptor separations (edge-edge distances d) in the modified proteins are 9.5 Å, His70; 12.7 Å, His48; and 15.5 Å, His83. Rates of photoinduced electron transfer in these ruthenium-modified myoglobins were measured by transient absorption spectroscopy. The ^(3)ZnP* → Ru^3+ rate constants are 1.6 × 10^7 (His70), 7.2 × 10^4 (His48), and 4.0 × 10^2 s^-1 (His83) (-ΔG°= 0.82 eV); charge-recombination (Ru^2+ → ZnP^+) rates are 1.1 × 10^5 (His48) and 7.3 × 10^2 s^-1 (His83) (-ΔG° = 0.96 eV). Activationless (maximum) rates assuming h = 1.3 eV are 7.2 X lo7 (His70), 3.3 × 10^5 (His48) and 1.8 × 10^3 s^-1 (His83). Distant electronic couplings, which limit the maximum rates in the modified myoglobins, have been analyzed along with data from Ru-modified cytochromes c in terms of a tunneling pathway model. Single dominant pathways adequately describe the electronic couplings in cytochrome c but do not satisfactorily account for the myoglobin couplings. The correlation of electronic coupling with tunneling length for myoglobin is improved significantly by the inclusion of multiple pathways.

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Winkler, Jay R.0000-0002-4453-9716
Gray, Harry B.0000-0002-7937-7876
Additional Information:© 1993 American Chemical Society. Received August 28, 1992. We thank David N. Beratan for helpful discussions, Atsuo Kuki for a preprint of ref 9b, Steven G. Boxer for the HuMb gene, and David G. Lambright, Steve R. Hubbard, and Wayne A. Hendrickson for providing us with the coordinates of a mutant human myoglobin. We are indebted to Thomas Sutherland for performing the large cell growth. J.L.C. acknowledges support from an NSF postdoctoral fellowship (CHE-9002195) and L.-L.W. thanks SERC (United Kingdom) for a NATO postdoctoral fellowship. This research was supported by the National Science Foundation, the National Institutes of Health, and the Arnold and Mabel Beckman Foundation.
Funding AgencyGrant Number
NSF Postdoctoral FellowshipCHE-9002195
Science and Engineering Research Council (SERC)UNSPECIFIED
North Atlantic Treaty Organization (NATO)UNSPECIFIED
Arnold and Mabel Beckman FoundationUNSPECIFIED
Issue or Number:4
Record Number:CaltechAUTHORS:20150430-135323908
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Official Citation:Casimiro, D. R., Wong, L. L., Colon, J. L., Zewert, T. E., Richards, J. H., Chang, I. J., . . . Gray, H. B. (1993). Electron transfer in ruthenium/zinc porphyrin derivatives of recombinant human myoglobins. Analysis of tunneling pathways in myoglobin and cytochrome c. Journal of the American Chemical Society, 115(4), 1485-1489. doi: 10.1021/ja00057a037
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57120
Deposited On:06 May 2015 14:57
Last Modified:10 Nov 2021 21:08

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