Magnetic Circular Dichroism and FTIR Studies of isolated Cyt b-559

Abstract

In the previous research the magnetic circular dichroism (MCD) spectra of spinach PSII reaction center was reported. The MCD spectra were found to be sensitive to the electronic state of the heme, and the shape and intensity of the spectra could be correlated with the redox state, the spin state and the axial ligation of the central metal atom. Here we report investigation of these effects in MCD spectra of purified Cyt b-559 (in oxidized and reduced) isolated from spinach and wheat. It was observed that the Cyt b-559 have MCD signals in 540-580 nm region and 400-440 nm region. The reduced purified Cyt b-559 exhibit visible MCD spectra very similar in shape and intensity to those of PSII reaction center in these regions. Thus these visible regions can serve as the major contributors for MCD of PSII reaction center and as a marker for the presence of reduced low-spin heme. We have observed that both the heme (at 1550, 1337 and 1239cm-1), the histidine ligands at 1104cm-1 and the protein (between 1600 and 1700cm-1and at 1545cm-1) are in line with previously reports. The results of FTIR and MCD measurements proved that His residues are ligands of heme in the Cyt b-559 and a -helixes are major kind of secondary structures in Cyt b-559. The above properties of Cyt b-559 purified from different higher plants are very similar.