NEAR-INFRARED SPECTRA OF SCAPHARCA HOMODIMERIC HEMOGLOBIN - CHARACTERIZATION OF THE DEOXY AND PHOTODISSOCIATED DERIVATIVES

The near-infrared charge transfer band at 760 nm (band III) has been i nvestigated in deoxy and photodissociated dimeric Scapharca hemoglobin . At 300 K, the 10-ns spectrum of the carbonmonoxy derivative photopro duct is shifted by about 6 nm toward longer wavelengths with respect t o the deoxy spectrum, both in buffer and in glycerol/buffer solutions, Moreover, the band III peak occurs at about the same wavelength at 30 0 K and at 10 K for the 10-ns photodissociated derivative, whereas in the deoxy derivative large changes in peak position and linewidth are observed as a function of temperature. These findings suggest that in dimeric Scapharca hemoglobin the photoproduct has not relaxed after 10 ns. The complete time dependence of the relaxation process has been s tudied both in buffer and in glycerol/buffer solutions at room tempera ture. The relaxation from the photoproduct to the deoxy species occurs on a microsecond time scale, in line with recent optical absorption a nd resonance Raman measurements.