Hemichrome formation during hemoglobin Zurich denaturation

Electron paramagnetic resonance (EPR) spectrum of hemoglobin Zurich, after oxidation, storage and heating, showed several absorption derivatives in the high field region (g approximately equal to 2) which are indicative of hemichrome formation. Characteristic visible spectra of hemichromes were observed for oxidized Hb Zurich and for its spontaneous precipitate. The proportional increase of EPR signals at g approximately equal to 2 and decrease at g = 6.37, the constant ratio of absorbance at 540 nm to 280 nm during heating, and the similarity of this ratio for spontaneously precipitated HbA and for Hb Zurich indicate that heme is not lost during the first steps of Hb Zurich denaturation.