Nitric oxide binding to ferrous native horse heart cytochrome c and to its carboxymethylated derivative: a spectroscopic and thermodynamic study.
Nitric oxide binding to ferrous native horse heart cytochrome c and to its carboxymethylated derivative has been investigated quantitatively by EPR and absorbance spectroscopy. The X-band EPR spectra and the absorption spectra in the Soret region of the nitrosylated derivative of ferrous native and carboxymethylated cytochrome c display the same basic characteristics reported for the beef heart cytochrome a3 in cytochrome c oxidase, and horseradish and baker's yeast cytochrome c peroxidase, as well as the high affinity form of oxygen carrying proteins. Values of the dissociation equilibrium constant for nitrosylation of ferrous native and carboxymethylated cytochrome c are 8.2 x 10(-6) M and < or = 5 x 10(-8) M, respectively, at pH 7.0 and 10 degrees C. The results here reported represent clearcut evidence for the nitric oxide-induced cleavage of the Fe-Met80 bond in ferrous native cytochrome c, and allow estimation of the free energy associated to the heme-iron sixth coordination bond (> 10 kJ mol-1, at 10 degrees C).
Ascenzi
P
P
Department of Pharmaceutical Chemistry and Technology, University of Turin, Italy.
Coletta
M
M
Santucci
R
R
Polizio
F
F
Desideri
A
A
D000818:Animals; D003574:Cytochrome c Group / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006736:Horses; D008745:Methylation; D009569:Nitric Oxide / Q000737:chemistry*; D011485:Protein Binding; D013053:Spectrophotometry; D013816:Thermodynamics
D003574:Cytochrome c Group; D009569:Nitric Oxide