Discussion 



149 



especially in aged extracts of mitochondria, a far better turnover. It 

 might be that one just fills up this phosphoprotein with ATP. Can you 

 say how much X there is in the system? 



'^Lehninger : We have not tried to determine this, but it must be a very 

 small amount ; as a guess I should say of the order of magnitude of the 

 molar concentration of the carriers. 



