Title

Double Integration and Titration of the Electron Paramagnetic Resonance Signal in the Molybdenum Iron Protein of Azotobacter vinelandii

Document Type

Article

Date of Original Version

1-1-1984

Abstract

The electron paramagnetic resonance (EPR) signal from the MoFe protein component of nitrogenase was doubly integrated over. the temperature range 2.2-15 K. Comparison of the protein double integral with that from the spin standard copper ethylenediaminetetraacetate demonstrated that two S = 3/2 spin centers are responsible for the observed EPR signal. The zero-field splitting parameter was found to be 15 ± 1 cm-1 from variation of the double integral with temperature. The double integral varied with the Mo content of the protein, suggesting direct Mo involvement in the S = 3/2 spin centers. EPR titrations using methylene blue, thionine, or dichloro-phenolindophenol as oxidants under a wide variety of solution conditions support previous results of three “P clusters”, two EPR centers, and a single center of a third but unknown type. © 1984, American Chemical Society. All rights reserved.

Publication Title

Biochemistry

Volume

23

Issue

13

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