Malate exchange between the cytosol and mitochondria.

1. By comparing the relative isotopic yields in glucose and CO(2) from precursors of mitochondrial and cytosolic malate, it is evident that the rate of isotopic exchange between these compartments is rapid. 2. A variety of potential inhibitors of malate exchange were tested, but no specific and effective inhibitor of the isotopic exchange has been found. 3. Compounds such as n-butylmalonate and p-iodobenzylmalonate, which have been used as inhibitors of the malate-phosphate transport system in isolated mitochondria, do not appear to be sufficiently specific to be useful in studies with intact cells.