COMPONENTS OF THE ENERGY-COUPLING MECHANISM 5 1 



State. However after the primary event there are certainly secondary events, which 

 follow the ATP-induced change, but it may take a certain finite lag period before 

 the rest of the very complicated mitochondrial structure undergoes those changes 

 which register as total light scatter. Does that make sense ? 



Ch.\nce : The facts are that we don't have fast ADP changes and the ATP ones 

 are slower. 



Jagendorf : When you restore DXP sensitivity to ATP : ADP exchanges by 

 mixing the isolated enzyme with fresh particles do you have to deplete these parti- 

 cles first ? 



Lehninger: Xo. They are already partly depleted. We can deplete them 

 further by exposing them to high salt concentrations or to glutathione. 



Jagendorf: Could this M-factor be a polynucleotide as in Pinchot's experi- 

 ments ? 



Lehninger: .Although M-factor is a heat-labile, non-dialysable substance, it is 

 possible that it carries a bound polynucleotide. We have tried polynucleotides and 

 at least with the polyadenylic acid and polyuridylic acid specimens we had they did 

 not work. 



Mitchell: I was very interested in Dr. Lehninger's concept of a mechano- 

 protein, but I would suggest that we need to take more care not to be too romantic 

 about this concept. We heard in the first discussion of this s>Tnposium (Dr. 

 Kendrew) how, during the uptake of oxygen, the haemoglobin molecule can be- 

 come reorientated and change shape ; and I suggest that in thinking about mechano- 

 proteins we should bear this example in mind as it illustrates the principle of change 

 of orientation implicit in the mechano-protein conception and is free of the 

 potentially misleading associations of the usual elastic catapult kind of model. 

 Perhaps it would be better to use the phrase "mechano-protein complex", because 

 we do not want to give the feeling that a change of shape and the contraction which 

 results is necessarily due to the contraction of individual protein molecules as we 

 used to think in the case of muscle. 



Lehninger: I completely agree that we should not be too precise about speci- 

 fying the mechanism. You are quite right, I would regard haemoglobin as an 

 example of a mechano-protein in this very general way. Obviously changes in 

 charge distribution or a dissociation are also possible molecular mechanisms under 

 this generic name. 



Azzone : You have tried to calculate the stoicheiometry between the moles of 

 HiO extruded from the mitochondria and the moles of ATP split. I wonder 

 whether it is necessary for ATP to be hydrolyzed or merely to be bound to the mito- 

 chondrial membrane. Do you think it is possible to inhibit the ATP-ase activity 

 and still maintain the ATP-induced contraction of the mitochondria ? 



Lehninger : As I said we are not prepared to state that ATP-ase activity is 

 necessary for the contraction ; contraction may require only binding of ATP, just as 

 in Morales' theory of contraction of actomyosin. Secondly, we have not found any 

 inhibitor or circumstances where we can inhibit ATP-ase without also inhibiting 

 contraction. 



