Paramagnetic effects in magnetic circular dichroism spectra of high-spin ferrous hemoproteins in the visible and near infrared spectral regions

Abstract

Magnetic circular dichroism spectra of high-spin ferrous hemoproteins (deoxyhemoglobin, deoxymyoglobin, ferroperoxidase and reduced cytochrome c oxidase) are compared for spectral region 350–800 nm at temperatures 293 - 10 K. At the lowest temperatures the MCD spectra over the whole spectral region are shown to be composed predominantly of the temperature-dependent C terms. The clear evidence are given for paramagnetic origin of positive MCD bands at about 760 and 680 nm and negative MCD band at about 630 nm associated with CT or d→d transitions. The C terms associated with these bands as well as those associated with π−π transitions in the visible Q band region are sensitive to the peculiarities in heme environment induced by protein conformation. In contrast, the Soret region MCD spectra of these proteins are very similar. The origin of C terms for porphyrin π−π* transitions is discussed in the framework of π−d π interaction suggested earlier for the explanation of C terms in the visible and Soret MCD of low-spin ferric hemoproteins [Mineyev AP, Sharonov YA (1978) Theor Chim Acta 49: 295–307]. The results and discussion illustrate the capability of C terms in near infrared and visible MCD in probing the active center in high-spin ferrous hemoproteins.