Comparison of human oxyhemoglobin in lyophilized form, red blood cells, and concentrated solution: the features of Mössbauer spectra and heme iron stereochemistry.

Mössbauer spectra of human oxyhemoglobin in red blood cells, concentrated solution, and lyophilized form were measured at 87 K. Additionally, Mössbauer spectra of lyophilized oxyhemoglobin were measured at 295 K. The values of quadrupole splitting appeared to be the same for oxyhemoglobin in red blood cells and concentrated solution and slightly lower than those of oxyhemoglobin in lyophilized form. The asymmetry of the Mössbauer absorption line shapes previously observed for oxyhemoglobin in red blood cells was also found for oxyhemoglobin in concentrated solution. These Mössbauer spectra were better fitted using two quadrupole split doublets with almost equal areas. In contrast, Mössbauer spectra of lyophilized oxyhemoglobin were symmetrical and satisfactorily fitted with one quadrupole split doublet. However, these spectra were also fitted with two quadrupole split doublets with equal areas. The variations of the absorption line shapes and parameters of oxyhemoglobin Mössbauer spectra were analyzed in terms of stereochemical differences of the heme iron and Fe(II)-O2 bond in alpha- and beta-subunits of tetrameric oxyhemoglobin.