244 



MAYNARD E. PULLMAN, HARVEY S. PENEFSKY AND E. RACKER 



for the particulate enzyme of mitochondria and phosphorylating mito- 

 chondrial fragments. Some of these properties are summarized in Table 

 III. While a number of divalent cations including Co + +, Mn + +, Fe + + 



TABLE III 

 Properties of ATPase 



Divalent cation required for activity 

 Stimulated by 2,4-dinitrophenol 

 Hydrolyzes ATP, ITP, GTP, and UTP 

 Inhibited by ADP but not IDP 

 Stoicheiometry : ATP + HoO^ADP + Pj 

 Exhibits "latent" activity phenomenon 



and Ca + + substituted for Mg + + in activating the enzyme, only Mg + + 

 and to a lesser extent Co + + gave rise to a dinitrophenol stimulation. The 

 enzyme hydrolyzed ITP, GTP, and UTP in addition to ATP. However, 

 it seems significant that only ATP hydrolysis was stimulated by dinitro- 

 phenol. Neither the nucleoside mono- nor diphosphates were hydrolyzed. 



O 



0-5 



10 1-5 2-0 



Preincubation time (hr) 



200 



Fig. I. Effect of preincubation temperature on ATPase and coupling activity. 

 The purified enzyme was preincubated either at o^ or 30. At the indicated time, 

 aliquots were removed and the appropriate activity measured at 30 as described 

 elsewhere [4]. 



The specificity of the ADP inhibition is of interest in view of the specificity 

 of this nucleotide in oxidative phosphorylation. The "latent" activity 

 phenomenon referred to in the table may actually be related to the well- 

 known "latent" properties of mitochondrial ATPase [8-10]. It was 



