Studies on the Electron Transfer System

The study of the terminal electron transfer system has been approached essentially in two ways. The first approach has been by way of the study of electron transfer in intact cells and in respiratory chain particles such as mitochrondria; it can best be exemplified by the studies of Chance and Williams (1). The second approach, which has been used in this laboratory, involves fragmentation of mitochrondria into subunits; their structural and functional characteristics are thus made more amenable to study (2). The first approach has been of great value in promoting understanding of the over-all kinetics and the sequence of the spectroscopically visible components of the respiratory chain, but it has made no contribution to the discovery of new electron transfer components such as coenzyme Q,’ nonheme iron, and copper. Furthermore, since the method relies entirely upon spectrophotometric evidence, it has not provided much information concerning the chemical character of the components of the system, their interaction, and their structural arrangement. The second method, on the other hand, has led to much new knowledge regarding the known components of the electron transfer system, the isolation of previously unknown components, as well as some insight into their interaction and structural arrangement. However, our recent studies suggest that fragmentation of the electron transfer chain by the methods in common use may be carried so far that the function and the structure of the complexes within the system are irreversibly destroyed. For example, it has not been possible so far to isolate cytochrome b and cytochrome cl in a form such that the oxidationreduction properties that they possessed in situ are retained. This is also true to some measure for preparations of the primary dehydrogenases. These two approaches to the study of the electron transfer system have now been extended by a third, which supplements the first approach and checks the limitations