94 LESTER PACKER 



system that the rate-limiting step with isolated mitochondria is ATP going out to 

 hexokinase, rather than ADP going back in to the mitochondrial phosphorylating 

 system. 



Packer: Of course very early in this study of the swelling-shrinking phe- 

 nomenon Raaflaub observed that the level of swelling in the mitochondria was 

 related to the intramitochondrial ATP level, but we may have to distinguish 

 between ATP which is bound and unavailable and that which is free, and this may 

 be the area where some of these discrepancies lie. 



AzzoNE : As far as I can understand the main discrepancy between your results 

 and those of Dr. Lehninger is that you get shrinking when mitochondria are in 

 State 3, that is when there is ADP in the medium and no high energy phosphate 

 intermediate(s) can accumulate in the mitochondria; when all the ADP in the 

 medium is transformed into ATP the mitochondria begin to accumulate high 

 energy phosphate intermediate(s) at the same time as they begin to swell. On the 

 contrary, in Dr. Lehninger's experiments, the mitochondria are swollen without 

 any addition to the incubation medium, and after addition of ATP they begin to 

 shrink. One possible explanation of this discrepancy is that in Dr. Lehninger's 

 experiments the mitochondria are completely uncoupled. Thus it would appear 

 that in uncoupled mitochondria external ATP is reqviired for shrinking whereas in 

 coupled mitochondria it is the presence of ATP and of high energy phosphate 

 intermediate(s) inside the mitochondria which causes swelling. 



