200 GIOVANNI FELICE AZZONE 



tions are required for transferring phosphate from this ATP to external 

 ADP. Indications were obtained for the following mechanisms being 

 operative in this transfer of phosphate : a double adenylate kinase, the 

 oxaloacetic carboxylase-pyruvic kinase and the activation of succinate 

 oxidation discussed in the present paper. An experiment showing the 

 effectiveness of these three mechanisms in transferring phosphate in order 

 to render ATP available to the DNP-induced ATPase is illustrated in 

 Table II. When ^-P-labelled mitochondria were incubated in the presence 



TABLE III 



Effect of Cysteine Sulphinate and Oxaloacetate on the Release of ^T 

 FROM Mitochondria during Incubation with Arsenate [7] 



Each tube contained in a final volume of 3 ml.: 0-05 M KCl, 0-03 M tris 

 buffer pH 7-5, 0-125 M sucrose, o-oi M MgCl., and, when indicated, 0-003 m 

 arsenate, 0-005 M cysteine sulphinate, 0-002 M amytal, 0-003 M oxaloacetate. 

 "^-P-labelled mitochondria" from 500 mg. liver. Time of incubation, 5 min. 

 Temperature, 30^. 



of DNP a partial release (about one-third) of the ^-P took place. Addition 

 of AMP, succinate or oxaloacetate enhanced the releasing effect of DNP. 

 No such effect was obtained with ^-hydroxybutyrate or glutamate, indicat- 

 ing that the release induced by succinate or oxaloacetate was not due in 

 an unspecific manner to the presence of an oxidizable metabolite. 



The capacity of oxaloacetate in removing ^-P from the mitochondria is 

 also illustrated in Table III. When the depleting effect of arsenate was 

 removed by the presence of amytal (see Fig. 4), addition of oxaloacetate 

 induced again a large release of ^^P from the mitochondria (Expt. i). 

 Oxaloacetate was able, alone or in the presence of amytal, to remove ^^P 

 from the mitochondria, and the depleting effect of oxaloacetate was 

 removed by the addition of cysteine sulphinate (Expt. i). A partial but 

 significant protection against the arsenate-induced release of ^^P from 

 labelled mitochondria was also obtained when cysteine sulphinate was 

 added to the incubation medium (Expt. 2). Thus the capacity of cysteine 



