Open AccessOptical, EPR and Mössbauer spectroscopic studies on the NO derivatives of cytochrome cd 1 from Thiobacillus denitrificans
Author(s) -
LIU MingCheh,
HUYNH BoiHanh,
PAYNE William J.,
PECK Harry D.,
DERVARTANIAN Daniel V.,
LEGALL Jean
Publication year - 1987
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1987.tb13605.x
Subject(s) - electron paramagnetic resonance , heme , chemistry , unpaired electron , crystallography , ferrous , cytochrome , absorption spectroscopy , nuclear magnetic resonance , photochemistry , inorganic chemistry , biochemistry , organic chemistry , physics , enzyme , quantum mechanics
We have used optical, EPR and Mössbauer spectroscopies to study the formation of heme‐NO complex upon the addition of nitrite to reduced cytochrome cd 1 from Thiobacillus denitrificans . The reduced d 1 heme binds NO under both alkaline and acidic conditions, but the binding of NO to the reduced c heme was strongly pH‐dependent. The Mössbauer data showed unambiguously that at pH 7.6 the c heme does not complex NO, whereas at pH 5.8 approximately half of the reduced c heme binds NO. This observation was confirmed by EPR studies, which showed that the spin concentration of the heme‐NO EPR signal increased from 2 spins/molecule at pH 8.0 to approximately 3 spins/molecuie at pH 5.8. Optical absorption study also showed strong pH dependence in the binding of NO to the reduced c heme. We have also analyzed the Mössbauer spectra of the ferrous d 1 heme‐NO complex using a spin‐Hamiltonian formalism. The magnetic hyperfine coupling tensor was found to be consistent with the unpaired electron residing on a σ orbital.