CHARACTERIZATION OF A 7FE FERREDOXIN ISOLATED FROM THE MARINE DENITRIFIER PSEUDOMONAS-NAUTICA STRAIN-617 - SPECTROSCOPIC AND ELECTROCHEMICAL STUDIES

A 7Fe ferredoxin, isolated from the marine denitrifier Pseudomonas nau tica strain 617, was characterized. The NH2-terminal sequence analysis , performed until residue number 56, shows a high similarity with the 7Fe ferredoxins isolated from Azotobacter vinelandii, Pseudomonas puti da, and Pseudomonas stutzeri. EPR and NMR spectroscopies identify the presence of both [3Fe-4S] and [4Fe-4S] clusters, with cysteinyl coordi nation. The electrochemical studies on [Fe-S] clusters show that a fas t diffusion-dominated electron transfer, promoted by Mg(II), takes pla ce between the ferredoxin and the glassy carbon electrode. Square wave voltammetry studies gave access to the electrosynthesis of a 4Fe cent er formed within the [3Fe-4S] core. The [3Fe-4S] cluster exhibited two reduction potentials at -175 and -680 +/- 10 mV and the [4Fe-4S] clus ter was characterized by an unusually low reduction potential of -715 +/- 10 mV, at pH 7.6. (C) 1996 Academic Press, Inc.