Open AccessElectron‐Spin Resonance of Nitrosyl Haemoglobins: Normal α and β Chains and Mutants Hb M Iwate and Hb Zürich
Author(s) -
TRITTELVITZ Eberhard,
GERSONDE Klaus,
WINTERHALTER Kaspar H.
Publication year - 1975
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1975.tb03903.x
Subject(s) - beta (programming language) , alpha (finance) , resonance (particle physics) , mutant , electron paramagnetic resonance , chemistry , nuclear magnetic resonance , physics , atomic physics , biochemistry , gene , medicine , computer science , construct validity , nursing , patient satisfaction , programming language
At 77 K the electron spin resonance (ESR) spectra of the NO derivatives of the mutant haemoglobins Hb M Iwate and Hb Zürich as well as of the isolated chains of normal haemoglobin were studied. Two types of ESR spectra differing in the g ‐value and the hyperfine splitting at g zz were observed. The type II spectrum is characterized by a hyperfine structure at g zz = 2.005 with a splitting constant of Δ H = 23 G ( 14 NO) or 32 G ( 15 NO), respectively. In the type I spectrum the splitting constant of the hyperfine structure at g zz = 2.009 amounts to Δ H = 18 G ( 14 NO) or 23 G ( 15 NO), respectively. In some cases this hyperfine structure is coincident with another one at g xx = 2.064 with nearly identical splitting constant. In addition, the type I spectrum is characterized by an increased ESR absorption at g xx = 2.064. At neutral pH the NO derivatives of the isolated chains as well as of the mutant haemoglobins give rise to a type II spectrum. In correspondence with previous results gained with normal NO haemoglobin, the ESR spectra of the NO‐α chains and NO‐Hb Zürich show a transition to type I in the acid region. This transition is favoured by binding of 2,3‐bisphosphoglycerate. On the other hand, the ESR spectra of the NO‐β chains and NO‐Hb M Iwate are of the type II also at acid pH. The NO‐β chains show a transition of the ESR spectrum from type II to type I only at alkaline pH. These results indicate that in the tetrameric NO haemoglobin only the a chains are responsible for the transition of the ESR spectrum from type II to type I in the acid region. The two types of ESR spectra are interpreted in terms of two kinds of haem‐NO complexes differing in the iron‐NO and iron‐imidazole distances. The type II spectrum is attributed to a complex with a relatively short iron‐imidazole distance which is responsible for a weakened σ‐bond in trans position. The type I spectrum arises then from a complex with a larger iron‐imidazole bond leading to an approach of the NO molecule to the iron. The influence of the protein conformation upon the iron‐imidazole bond length is discussed with regard to the ESR spectra of the mutant NO haemoglobins and considering the influence of agents modifying the protein structure.