Magnetic circular dichroism and magnetooptical rotatory dispersion of submitochondrial particles at room and liquid nitrogen temperatures

Abstract

Magnetic optical activity methods magnetooptical rotatory dispersion (MORD) and magnetic circular dichroism (MCD) [ 1 ] proved to be a useful tool in studies of certain heme proteins, such as myoglobin, hemoglobin [2-41, cytochrome c [S--7] , b2 [8,9] , b5 [9] and also in experiments with a model systems [IO-121 . MORD and MCD are sensitive to heme iron oxidoreduction transitions as well as to heme surrounding and the nature of axial ligands in heme proteins [4,11,12]. High resolution power of these methods provides an advanced opportunity for investigation of multienzyme systems, which cannot be resolved into individual components without a concomitant loss of activity and/or native structure of these components. Mitochondrial respiratory chain belongs to this type of integral system. Difference absorption spectroscopy [ 131 is one of most commonly used optical methods in studies of cytochrome components of mitochondria or submitochondrial particles (SMP). However, the individual absorption bands of several b-type cytochromes and cytochromes (c + cl) present in respiratory chain are overlapped significantly in Q-, /3and y-regions and can not be well resolved even in low temperature spectrophotometric measurements. We now want to demonstrate here the advantage of MORD and MCD methods when applied to the studies of SMP cytochrome chain. It will be shown that MCD and MORD effects arising from reduced band c-type cytochromes are almost completely