110 



anisms because little is known about them. I think I can say again that the 

 whole business of radiation effect is entirely dependent first of all upon what 

 happens in the non-radiation system; for instance, nobody can tell us how pro- 

 tein is synthesized and, therefore, how radiation would affect the synthesis of 

 protein. 



POLLARD: There is a very interesting speculation as to how protein is 

 synthesized and it looks pretty good; namely, that the bigger helix of the nucleic 

 acid just encloses the protein and specifically determines its structure. 



KAMEN: Well, nobody has a function for nucleic acid in the biological sys- 

 tem. It is there, but no one knows why. This speculation about the connection 

 between nucleic acid and protein is an old one. In fact, I am among the many 

 who at times have written papers about it. But I don't think we should deal at 

 length here with anything about which we know so little. 



Let's put it this way as far as biological substances are concerned. What 

 distinguishes the biology from the chemistry is the cooperative action of cellu- 

 lar substances, and certainly there is where you have to look for part of the ex- 

 planation of radiation effects. On the other hand, the isolated system has to be 

 studied first before it is possible to imagine cooperative effects. What is known 

 about the radiochemistry of surface films or interfaces? Dr. Mazia knows 

 about this and I think probably he is the only one here or one of the very few 

 in the country who has experience with this subject. Since practically all of the 

 biological systems we deal with involve interfaces and most of the activity of 

 enzymes takes place between the liquid and the solid state, it appears quite 

 obvious that data are needed on this. I wonder whether Dr. Mazia can tell us 

 about radiation effects on surface films. 



MAZIA: What impressed me first in the studies of radiation effects on sur- 

 face films containing enzymes was their enhanced sensitivity to inactivation by 

 radiation. The systems we have studied most intensively is a pepsin-albumin 

 complex spread over water. We can maintain it at a pH at which the enzyme is 

 inactive, irradiate it, then measure the rate at which it digests itself when we 

 shift to a pH at which pepsin is_ active. A few hundred roentgens suffice for 

 large scale inactivation. The interpretation of such experiments raises some 

 of the questions that Dr. Kamen must have in mind. The film is a two-dimen- 

 sional continuum having the mechanical properties of a solid or gel of mono - 

 molecular thickness. All the molecules are interlocked, and you no longer 

 know how to define an individual molecule. Therefore, you cannot really speci- 

 fy the unit that participates in a single event of inactivation. It might consist 

 of what, in a solution, would be many molecules and this may account for the 

 seemingly high efficiency of inactivation by X rays. 



The other important question is the relation of the proteins to the water in 

 the system. By spreading a protein over water, you partially unfold the mole- 

 cules, increase the area of protein that is in contact with the water of the medi- 

 um, and reduce the chances that part of the material will protect the rest 

 against radicals. Such situations might exist in biological systems. 



Recently, Miss Blumenthal and I have attempted to evaluate the role of 

 spreading as such versus the role of water by studying the inactivation of dry 

 catalase films deposited on solid surfaces. We compared the inactivation of 

 films formed by first spreading the catalase on an air-water interface and then 

 depositing on glass with the inactivation of films formed merely by drying down 

 catalase solutions on glass. By "drying" we merely mean a condition achieved 

 in a desiccator over "Drierite". While the data are limited, it looks to us as 



