Glycolysis and the Pasteur Effect 215 



which utilizes either ATP itself or a compound which requires 

 ATP for synthesis. It includes also the enzymes which cleave 

 ATP to AMP and pyrophosphate, since pyrophosphatase and 

 adenylic kinase (mi/o-kinase) which generate Pi and ADP 

 from pyrophosphate and AMP are universal cellular compon- 

 ents. It includes also the enzymes which simply hydrolyse 

 ATP to ADP and Pi, although some doubts have been ex- 

 pressed as to whether these "wasteful enzymes" function 

 intracellularly in this manner. 



It has been mentioned before and emphasized by Lynen 

 and Koenigsberger (1951) that in a steady state the rates of 

 cellular phosphorylation and dephosphorylation must be 

 equal. Since we have found it quite difficult in our recon- 

 structed systems to balance accurately the phosphorylating 

 enzymes by the addition of ATPase, our already boundless 

 admiration of Nature's accomplishments has received a 

 further stimulus. How do cells maintain the oxidative and 

 glycolytic rates under such a variety of conditions and adjust 

 ATPase activity to follow suit? We have no real answer to 

 this question, but feel vaguely that the fashionable feedback 

 mechanisms play a significant role. We have some clues from 

 our cell-free system as to how ATPase activities might be 

 adjusted, but no clues as to whether these mechanisms are 

 operative intracellularly. We have observed that a mito- 

 chondrial ATPase, which is minimal when assayed by con- 

 ventional procedures, can be made to manifest itself by the 

 continuous removal of ADP. This can be accomplished by an 

 ATP-regenerating system consisting of phosphoenoZpyruvate 

 and pyruvate kinase. ADP, which is known to inhibit ATPase 

 activity (Kielley and Kielley, 1953) can be thus visualized to 

 regulate the breakdown of ATP. If such a mechanism 

 operates in respiring mitochondria, this ATPase activity 

 should increase during oxidative phosphorylation. It is not 

 relevant for this concept whether mitochondrial ATPase 

 catalyses a truly hydrolytic reaction or is a metabolic expres- 

 sion of some work that has been accomphshed, e.g. transport 

 of potassium. Even if the mitochondrial ATPase activity 



