Suiuinary and Discussion 



Linus Pauling, Chairman 



California Institute of Technology, Pasadena, Calif. 



I HAVE THE TASK of Summarizing the work that has been reported by the 

 speakers. 

 Since this symposium is on the subject of biological specificity, the first 

 question that we ask is: What is biological specificity? 



Electron micrographs and X-ray diffraction patterns of tobacco mosaic virus 

 show that the rods that constitute the virus particles have the form of a cylin- 

 drical tube of protein, within which are strands of nucleic acid. The tube of 

 protein is made up of small protein molecules, molecular weight of the order 

 of 20,000, which are arranged in a helix. We conclude that certain protein mole- 

 cules are manufactured that have the power of clamping onto one another in a 

 specific way, so as to produce a tightly wound helix. The power that these pro- 

 tein molecules have, that of clamping onto identical molecules to produce a 

 helix with well-defined diameter and pitch, represents one sort of biological 

 specificity. 



The ability that genes have to duplicate themselves and also to control the 

 manufacture of protein molecules, such as those in tobacco mosaic virus, repre- 

 sents another sort of biological specificity. The action of enzymes, discussed 

 by Drs. Wilson, Anfinsen, and Alberty, represents another special sort of biologi- 

 cal specificity. Still another sort is represented by the interaction of antibodies 

 and antigens. 



This last aspect of biological specificity was discussed by Drs. Pressman and 

 Haurowitz. A great deal of information about the specific interactions of anti- 

 bodies and antigens has been obtained through the study of serological reac- 

 tions; in particular, there have been extensive studies of the action of simple 

 substances that act as inhibitors of serological reactions, by combining with 

 antibodies. Serological systems may not be as good as enzyme systems for the 

 study of biological specificity, because the antibodies present in an antiserum 

 are not all identical: the antiserum is heterogeneous, whereas a preparation of 

 an enzyme may be essentially homogeneous. Nevertheless a great deal of evi- 

 dence about the nature of the specific interactions of antigens and antibodies 

 has been obtained through the study of serological systems. It was as the result 

 of the study of serological systems, especially by Landsteiner, that 25 years 

 ago Professor Haurowitz and Dr. Breinl, and independently Stuart :\Iudd and 

 also Jerome Alexander, simultaneously suggested the important idea of com- 



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