Abstract
The electron spin resonance (ESR) spectra of 15NO- and 14NO-ligated Hb Kansas have been measured at 77 K in the range of pH 5 to 10. At low pH the ESR spectrum is the composite of a type I and a type II spectrum which changes to another composite of a type I and type II spectrum at high pH. For the definition of type I and type II spectra and the correlation of these types with two tertiary conformation states see Overkamp et al., Z. Naturforsch. 31 c , 524 [1976]. Both, the type I and the type II spectra observed at low and high pH respectively are different with regard to g-tensors and hyperfine-splitting constants. Therefore at intermediate pH values the ESR spectra of NO-Hb Kansas are the composites of four spectral
components.
The assignments of the four spectral components to the a and the β chains are arrived at from the comparison of the ESR spectra of the α2Mmet β2NO and of the α2MNO β2NO species of Hb M Iwate. α and β chains are both characterized by a pH-dependent spectral transition from a type I to a type II spectrum. The chains are non-equivalent with regard to both the type I and the type II spectra. The type I spectra assigned to the a and the β chains are characterized by g*zz = 2.0095 with a hyperfine splitting of
a*zz (15NO) = 2.36 mT and gzz = 2.0085 with a hyperfine splitting of a*zz(15NO) = 2.41 mT respectively. The type II spectra assigned to the α and the β chains are characterized by g*′zz = 2.005 and a hyperfine splitting of a*′zz (15NO) = 3.07 mT and g′zz=2.005 and a hyperfine splitting of a′zz (15NO) = 3.31 mT.
The change of the hyperfine splitting at gzz during the transition from type I to type II corresponds to an increase of the spin density at the NO by about 25% in both types of chains. Comparison of type I spectra of the NO-ligated α and β chains respectively demonstrates that the spin density at the NO is larger in the β chains than in the oc chains.
The spectral types are correlated with functional states defined by the kinetics of NO-binding.
Binding of inositol hexaphosphate has no influence on the ESR spectra in the whole range of pH as it is expected if NO-Hb Kansas is in the quaternary T structure.
Strong reduction of the Korringa relaxation in the spin-density wave regime ofEuFe2As2observed by electron spin resonance