Cofactor and metal requirements of brain mitochondria

Abstract

In recent years much effort has been devoted to the localization of vital processes within cells, especially in the mitochondria. Methods for the isolation of mitochondria have been worked out for many tissues and have shown that the general properties of these units do not vary greatly from one tissue to another. A problem of great interest is their survival outside the cell. Working with isolated brain mitochondria we have measured the rates of oxidation of substrates of the tricarboxylic acid cycle and the process of oxidative phosphorylation and employed them as indicators of the survival of mitochondria as effective units. We find that their survival time is short but may be prolonged by the addition of a number of soluble factors. These include adenosine triphosphate, coenzyme I, glutathione, cobalt and what is believed to be a new cofactor. A remarkable feature of these substances is the complex interrelationship they display. Thus cobalt is relatively ineffective in the absence of glutathione, while the latter has no influence in the absence of cobalt. The new factor resembles glutathione in this respect. Even in combination these three cofactors require the presence of both adenosine triphosphate and coenzyme I to produce their full effect. Another metal, copper, may be of importance, since it antagonizes the action of cobalt and its inhibitory effect may be abolished by raising the concentration of cobalt. These coenzymes are ineffective unless they are added to the mitochondria at the start of the incubation in the Warburg bath. We suggest that they are concerned in some process which is important in the preservation of the integrity of the mitochondrial particles.