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. Thermodynamical parameters are determined for the hexa- and penta-coordinated cases.