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Isolated iron-molybdenum cofactor of nitrogenase exists in multiple forms in its oxidized and semi-reduced states

Authors :
Newton, W E
Gheller, S F
Feldman, B J
Dunham, W R
Schultz, F A
Source :
Journal of Biological Chemistry; February 1989, Vol. 264 Issue: 4 p1924-1927, 4p
Publication Year :
1989

Abstract

Electrochemical and EPR spectroscopic experiments demonstrate that the isolated iron-molybdenum cofactor from the molybdenum-iron protein of nitrogenase from Azotobacter vinelandiiexists in multiple forms in both its oxidized and semi-reduced states. The particular forms found in either oxidation state appear to be a function of the acid/base status of the solvent, N-methylformamide. In “alkaline” N-methylformamide, a single, detectable form of iron-molybdenum cofactor is observed for both oxidized and semi-reduced states. The semi-reduced form, termed R(s-r), is the one previously recognized with an S= 3/2 EPR spectrum with apparent g values of 4.6, 3.4, 2.0. Its oxidized counterpart, termed B(ox), is characterized electrochemically by a differential pulse voltammetric reduction peak at −0.37 V versusthe normal hydrogen electrode. In “acidic” solvent, two distinct, previously unrecognized redox pairs of iron-molybdenum cofactor forms exist. The two semi-reduced forms, N(s-r) and W(s-r), are characterized by EPR spectra with g= 4.5, 3.6, 2.0 and g= 4.9, 3.1, 1.9, respectively. Their oxidized counterparts, A(ox) and C(ox), have differential pulse voltammetric reduction peaks at −0.32 and −0.43 V versusthe normal hydrogen electrode, respectively. Manipulations of either the isolation protocol or the sample conditions affects both the type and distribution of forms present. Each form likely corresponds to a biologically significant state of the cofactor cluster within the protein.

Details

Language :
English
ISSN :
00219258 and 1083351X
Volume :
264
Issue :
4
Database :
Supplemental Index
Journal :
Journal of Biological Chemistry
Publication Type :
Periodical
Accession number :
ejs55939588
Full Text :
https://doi.org/10.1016/S0021-9258(18)94121-9