NDLI: Electrostatic effects in electron transfer reactions of [2Fe-2S] ferredoxins with inorganic reagents.

Content Provider	PubMed Central
Author	Vidakovic, M. Germanas, J. P.
Abstract	The kinetics of electron transfer from the reduced [2Fe-2S] ferredoxins from the cyanobacterium Anabaena 7120 and the protozoan Trichomonas vaginalis to select cobalt coordination compounds have been studied in order to gain insight into the mechanism of electron transfer and intrinsic reactivity of [2Fe-2S] active sites. With tripositive cobalt complexes, reactions of both proteins displayed saturation kinetics; values of association constants of 12,900 and 1,400 M-1 and limiting rate constants of 7.6 and 3.5 s-1 were found for oxidation of T. vaginalis and Anabaena ferredoxins, respectively, by Co(NH3)6(3+) at room temperature and I = 0.1 M. An activation enthalpy of 12.1 kcal/mol and activation entropy of -14.3 cal/mol K for oxidation of T. vaginalis ferredoxin by Co(NH3)6(3+) contrasted with corresponding values of 13.4 kcal/mol and -10.5 cal/mol K for the Spirulina platensis protein, which is homologous to Anabaena ferredoxin. The dependence of the reaction rates on ionic strength were measured to probe the importance of electrostatics on the reactivity of the proteins. Analysis of the ionic strength dependence of the oxidation of the proteins by Co(NH3)6(3+) by the "parallel plate" model of Watkins et al. (1994, Protein Sci 3:2104-2114) afforded values for active site charges of -0.7 and -1.1 and limiting rate constants at infinite ionic strength of 25,800 and 76 M-1 S-1 for T. vaginalis and Anabaena ferredoxins, respectively. These results suggest that the [2Fe-2S] center of the protozoal ferredoxin is more accessible and adjacent to a less highly charged, more compact patch of negative charges than the photosynthetic protein.
Related Links	http://dx.doi.org/10.1002/pro.5560050905
Ending Page	1799
Page Count	7
Starting Page	1793
File Format	PDF
ISSN	09618368
e-ISSN	1469896X
Journal	Protein Science : A Publication of the Protein Society
Issue Number	9
Volume Number	5
Language	English
Publisher	Cold Spring Harbor Laboratory Press
Publisher Date	1996-09-01
Access Restriction	Open
Rights Holder	Cold Spring Harbor Laboratory Press
Subject Keyword	Biochemistry Molecular Biology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Medicine Molecular Biology Biochemistry

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