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The characterization and magnetic properties of the azide and imidazole derivatives ofPseudomonasnitrite reductase

Authors
Journal
Journal of Inorganic Biochemistry
0162-0134
Publisher
Elsevier
Publication Date
Volume
14
Issue
1
Identifiers
DOI: 10.1016/s0162-0134(00)80010-0
Disciplines
  • Biology

Abstract

Abstract Optical absorption, mcd, and epr spectroscopy have been used to characterize the azide and imidazole derivatives of oxidized Pseudomonas nitrite reductase. At pH 7.0 azide binds solely to heme d 1 with an affinity constant, K aff = 360 M −1, whereas imidazole binds to both hemes c and d 1 with k aff = 35 and 55 M −1, respectively. Low-temperature mcd and epr spectroscopy indicate that c and d 1 are low-spin ferrihemes in both derivatives, although the epr of the heme d 1-azide component is very weak and requires explanation. Attempts to obtain a high-spin heme d 1 in the intact enzyme using the weak field ligands fluoride and thiocyanate have proved unsuccessful. Electron paramagnetic resonance experiments involving an oxidized enzyme derivative in which heme d 1 is complexed by NO, and hence epr silent, have enabled unambiguous assignment of the epr spectrum of Pseudomonas nitrite reductase.

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