MAGNETIC CIRCULAR-DICHROISM OF HEMOPROTEINS

This chapter describes the progress made over the last 10 years in studies of the magnetic circular dichroism (MCD) spectra of heme models and proteins. The construction by Oxford Instruments of a split-coil superconducting magnet, in which the sample could be immersed in a liquid helium bath, necessitated the development of optical windows that remained strain free and capable of propagating circularly polarized light at 4.2 K. This led to the ability to make measurements routinely on samples of hemoproteins over the temperature range 1.5–300 K and up to fields of 6–7 T and opened the way for the measurement for the first time of MCD magnetization curves of metalloproteins and hence the methodology for the study of the ground-state magnetic properties of individual heme centers in proteins. It is now possible to measure the MCD spectra of hemoproteins in a solution of water and cryoprotectant mixtures over the wavelength range 195–5000 nm at magnetic fields up to 10 T, with good sample temperature control over the range 1.5–300 K. Although MCD studies in the vacuum ultraviolet region have been carried out using laboratory-based instruments and synchrotron sources, no reports have appeared of the spectra of hemoproteins in this wavelength region. © 1991 Academic Press, Inc.