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DISCUSSION 



Brachet: Prof. Krebs, would you comment on the possible role of cell 

 structure in this regulatory activity of the cell? 



Krebs: A recent number of Nature contains a letter by Prof. Peters on 

 this point (1956, Nature, Lond., Ill, 426). He discusses the possible 

 role of what he calls the cytoskeleton of the cell, a hypothetical network 

 of structures which keeps enzymes and substrates in their places. He 

 suggests that hormones may change the nature of this cytoskeleton and 

 that hormones may not act directly on a specific enzyme ; that perhaps 

 one hormone can act on a number of enzymes at the same time, by 

 making substances accessible. This is perhaps a useful working hypo- 

 thesis, but it is difficult to visualize how one can test this idea by 

 experiments. I would certainly agree that the structure is a very 

 important point. 



Alexander: I would like to ask a very similar question, but phrased 

 in a slightly different way. You have told us that in the whole chain of 

 enzyme reactions there are certain pacemakers. Now there must be a 



