[Study of the complex of myoglobin with nicotinic acid by the method magnetic circular dichroism. Nature of the double hemochromogen].

The complex formed by myoglobin and nicotinic acid exhibits unusual spectral properties. Instead of the usual two bands in the visible region the complex shows four bands assigned to the so called twin hemochromogen. Some attempts were previously made to clarify the nature of the twin hemochromogen, but the interpretation given was somewhat doubtful. We have shown that the combination of two spectral methods, namely magnetic circular dichroism and absorption spectra, give evidence that unusual absorption spectrum of the myoglobin complex with nicotinic acid is not attributed neither to the presence of the other hemochromogen nor to the soft vibrations but is due to the strong splitting of the pure electronic Q00 band into two Qox and Q0y bands. The splitting is caused by the distortion of heme structure by its asymmetrical environment.