In our previous papers it has been reported that charactaristic glutamic pyruvic transaminase (GPTM) and glutamic oxalacetic transaminase (GOTM) located at mitochondoria have quite different natures from those in nonparticulate fraction. It was elucidated the significance of their localization in mitochondoria from the view point of the coupling reaction with TCA-cycle in this paper. The data presented in this paper indicate that C^<14>-glutamic acid, when added to mitochondrial preparations, is rapidly converted into C^<14>-aspartic acid attended with C^<14>O_2 release stoichiometricaly. In this system malonate inhibited the formation of C^<14>-aspartate and hydroxylamine at a very low concentration, at which it did not inhibit the oxidation of α-ketoglutaric acid and glutamic dehydrogenase activity, also strongly inhibited the production of C^<14>-aspartic acid. These data indicated that the convertion of glutamate to aspartate in mitochondria was an altanative coupling reaction between GOTM and a half of TCA cycle as Krebs's suggestion. In the same way aspartate and acetate added was converted into glutamate. No detectable amount of C^<14>-glutamate was found from C^<14>-α-ketoglutarate which was supplied from TCA-cycle, when ammonia, C^<14>-acetate and succinate were added to mitochondrial preparations, though much amount of glutamate was detected, when ammonia, acetate, succinate and α-ketoglutarate were added as substrates. These data suggested that glutamic dehydrogenese could not react with α-ketoglutarate formed in TCA-cycle but could react with it added from outside of mitochondria. The following unit reaction of GOTM would be expected to occur between oxalacetate located at TCA cycle and aspartate added from outside of mitochondria. Aspartate + C^<14>-Oxalacetate &rlarr; Oxalacetate + C^<14>-Aspartate. Cold aspartate, when added C^<14>-succinate only to mitochondria was converted into C^<14>-aspartate strongly. The same kind of reaction of GOTM at glutamate and α-ketoglutarate could be recognized.