17 



just what can bring an end to this random walk. That is, what sort of setup 

 could there be in some part of the molecule where this process could finally re- 

 sult in something irreversible. The thing surely does not keep on bouncing back 

 and going the other way. 



POLLARD: That is why I tried to relate this to Augenstine's idea of 

 denaturation. I must admit that his idea of the sulfur bond breaking and a new 

 sulfur bridge forming may be satisfactory, but there are molecules in which this 

 is unlikely, e. g. , molecules that contain no sulfur. So I felt that there must be 

 a variety of ways of reforming bonds. My feeling is that the same atoms in 

 every protein molecule are capable of being bound in different ways; that they 

 don't have to be uniquely bound as proteins. My idea is that this migrating, weak 

 bond, if you like, merely gives an opportunity for some of these other things to 

 form, and if they do, then you have the loss of biological function. If they don't 

 then you have recovery. In cases, for instance, like bovine serum albumin 

 where it takes three ionizations to produce the inactivation, it is obvious that 

 one ionization will do nothing. It has the chance of doing something, but on the 

 whole, 1 ionization is not sufficient. But with 3, apparently this multiple proba- 

 bility of something happening may cause the inactivation. 



Hutchinson (11), who discovered this effect of bovine serum albumin, 

 thinks that a great part of solubility loss is due to multiple ionization. The proof 

 is not complete, but, in this session, we have to talk about hunches. 



MAZIA: It seems to me that what you need are experiments where you 

 can assess the effects of radiation on two measurable activities of the same 

 molecules that you know to be located in different parts of the molecule. One 

 case that comes to mind where I think that the measurement would be possible 

 is myosin. Szent-Gyorgyi has shown that myosin i=; an association of two 

 entities which he calls meromyosins, and which are linked together by peptide 

 bonds. One of these sub-units has an enzyme activity -- splitting ATP -- and 

 the activity of the other can be measured as contraction. It would be predicted 

 here that the radiation effects on the two activities would be parallel, would it 

 not? 



POLLARD: Yes, that should be the case. That is a good experiment. 



BARRON: You can decrease the activity of myosin by irradiation and 

 you can bring it back. In other words, the only thing you do is to oxidize the 

 sulfhydryl groups without destroying the architecture of the molecule. 



POLLARD: That again, however, would apply to indirect processes. 

 That is one difficulty. 



BARRON: Unfortunately, in reality you have to remember that the 

 biological system contains 80 percent water saturated with oxygen; therefore, if 

 you are interested in biology you have to think with this in mind. 



MAZIA: But for the purpose of testing this theoretical formulations, it 

 seems likely that you could irradiate in the dry condition. 



BARRON: You cannot dry myosin and have it contracted. 



MAZIA: Well, you could soak it in glycerol and serve the same pur- 



pose. 



BARRON: Then you oxidize the glycerol. 



