Use of Radioactive Isotopes in Studying the Metabolism of Mitochondria

Abstract

This article will be restricted to the use of isotopes in those aspects of mitochondrial metabolism which are truly specific for mitochondria and for which isotopes have proved to be particularly useful tools. These categories include the turnover of mitochondrial components, the concentration and turnover of lowmolecular-weight compounds and ions by mitochondria, and the synthesis and turnover of adenosine triphosphate (ATP) by the mitochondria. Now, at first glance it would appear that the use of isotopes in many of these cases is redundant to the use of previously-used biochemical methods, for we can measure an increase in the amounts of many of the mitochondrial products of metabolism. However, as in the case of investigations into other aspects of metabolism, it has been found that measurements of the net syntheses or degradations of compounds tell us only little about the intermediate reactions involved. Thus, the use of isotopes has made it possible to discern, first, that there are indeed intermediate steps involved, and secondly, has led to much more detailed information concerning metabolic sequences. I hope to illustrate these points as I consider the various aspects I have outlined above; particularly, the use of isotopes in elucidating the mechanism of oxidative phosphorylation by mitochondria. Because of the great number of papers involved with mitochondrial metabolism, the bibliography, while complete with regard to papers in which the use of isotopes has been mentioned, will be only partially complete with reference to other papers in which no isotopes were used.