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Professor Klotz: With respect to your last remark, Dr. Anfinsen, I may say- 

 that I believe that hemoglobin, which dissociates into halves in urea still picks 

 up oxygen in urea just as well as before. I know that this is true also of hemo- 

 cyanin but with respect to hemoglobin I think there are no disulfide bridges. 

 All the sulfur can be shown to be in the form of sulfhydryl groups. 



Would you care to comment on how you visualize a structure like that? Par- 

 ticularly, I wonder if it is fair to limit your comment just to small molecules 

 like ribonuclease and pepsin? 



Dr. Anfinsen: I am sorry I introduced that point at all. It is not what I 

 wanted to say. Perhaps the first catalyst was simply the heme. 



Professor Klotz : I did not want to go into that so much as into the assump- 

 tion that in urea the molecules really unfold. Again I raise the question wdth 

 with respect to the hemoglobin and the general question of what happens in 

 urea. In this case, in hemoglobin, you cannot say that the disulfide bonds are 

 holding the structure together, because there are not any, so the hydrogen bonds 

 must be holding it together. Can we be sure then that in urea you are really 

 breaking these hydrogen bonds — that the inactivation presumably occurs by 

 the breaking of hydrogen bonds? 



