Proton electron nuclear double resonance from nitrosyl horse heart myoglobin: the role of His-E7 and Val-E11.

Electron nuclear double resonance (ENDOR) spectroscopy has been used to study protons in nitrosyl horse heart myoglobin (MbNO). (1)H ENDOR spectra were recorded for different settings of the magnetic field. Detailed analysis of the ENDOR powder spectra, using computer simulation, based on the "orientation-selection" principle, leads to the identification of the available protons in the heme pocket.

Temperature dependence of Q-band electron paramagnetic resonance spectra of nitrosyl heme proteins.

The Q-band (35 GHz) electron paramagnetic resonance (EPR) spectra of nitrosyl hemoglobin (HbNO) and nitrosyl myoglobin (MbNO) were studied as a function of temperature between 19 K and 200 K. The spectra of both heme proteins show two classes of variations as a function of temperature. The first one has previously been associated with the existence of two paramagnetic species, one with rhombic and the other with axial symmetry.

Contribution of Electron Paramagnetic Resonance to the studies of hemoglobin: the nitrosylhemoglobin system.

Since the initial work of Ingram (8,10) Electron Paramagnetic Resonance contributed considerably to research in hemoglobins. Now, 40 years later we review some of the results of the application of EPR to nitrosylhemoglobin (HbNO), as an example of the diversity of information which this technique can provide.

Nitrosyl hemoglobins: EPR above 80 K.

The EPR spectra of nitrosyl hemoglobin and myoglobin in different conditions (native, denatured and lyophilized), as well as of hematin-NO were obtained in the temperature range of 80-280 K. There is a substantial and reversible decrease of the areas of the EPR spectra of all the hemoglobin samples above 150 K. The interpretation of the results implies the existence of two conformational states in thermal equilibrium, only one of which is EPR detectable.