SESSION VII, DISCUSSION 655 



account for the evolution and development of the extreme variety of living creatures, may 

 be explained, to a considerable extent, by the fact that the combination of these substances, 

 the spatial arrangement and sequence of these reactions in time, can be infinitely various 

 In a collection of very similar and uniform substances. I should like to remind you of 

 Prof. Hinshelwood's formulation that in the cell there is a collection of more or less 

 constant structures, while, at the same time, there is an extreme variety in the quantitative 

 relationships between them. 



I believe that for further sjmiposia we shall want, not only an extension of our informa- 

 tion on the conditions of formation of carbohydrates, nucleoproteins and other substances, 

 but also of that concerning the basic laws governing the networks of chemical reactions 

 in the open systems which led directly to the formation of life. 



S. Miller: I should like to take up the question of the origin of life at high temperatures. 

 Life is in general characterized by lability to heating. The organic compounds of which 

 the hving organism is made up, nucleic acids, sugars, polysaccharides and proteins, are 

 also characterized by lability to heating. When organic substances were heated under 

 geological conditions they were heated for a very long time. It is hard to understand 

 how the complexes of living structures of which living organisms must have been made 

 up could have survived for long geological periods under conditions of high temperatures. 



The hypothesis that the chemistry of the time before the beginning of life must have 

 been similar to contemporary biochemistry is a great simplification of the reactions which 

 took place in the earliest stages. I should Uke to emphasize that this hypothesis is not 

 inevitable. Chemical processes occurring before and after the formation of enzymes must 

 have been very different from one another both qualitatively and quantitatively. Let us 

 consider, for example, the transamination of oxaloacetic acid with the formation of aspartic 

 acid. In the absence of a sufficiently active catalyst to speed up the reaction, aspartic acid 

 will, in general, not be formed because oxaloacetic acid is spontaneously decarboxylated 

 at an appreciable rate. Thus, in the presence of a catalyst, aspartic acid is formed while, 

 in the absence of a sufficiently active catalyst, it is not formed at all. I think that this 

 example supports the idea that there was a qualitative diff'erence in chemistry before and 

 after the origin of enzymes. 



K. MoTHES : So far as we know the conditions for the existence of living things at, for 

 example, 85 °C are not limited by the fact that nucleic acids and proteins are denatured 

 at high temperatures, but by the fact that, in hot springs, all metabolism becomes ex- 

 tremely difficult. Theoretically one may imagine that Ufe has many forms which differ 

 among other things in their response to a rise in temperature, and it cannot be affirmed 

 categorically that Hfe is necessarily characterized by being associated with a material which 

 is denatured within the range 50-60 C 



L. Pauling: I suggest that consideration of the question of the nature of proteins 

 could be continued. In particular, I think it would be good if the question were more fully 

 clarified from a theoretical point of view. 



We know that, in general, proteins are molecules which can be denatured by various 

 means, among them heating. It is certainly hard to construct a protein which will serve 

 as an enzyme and yet will not be denatured by the temperature of the body. Let us sup- 

 pose that we have an organism which produces proteins which are stable at one par- 

 ticular temperature. If the body temperature then falls and remains low for long enough, 

 then the organism may change, mutating in such a way that its proteins are stable at the 

 new lower temperature and unstable at the former temperature. 



This would not involve any increase in complexity of the organism in the new conditions. 

 I think therefore that, owing to the nature of protein molecules, there is nothing surprising 

 in the fact that many proteins are stable at body temperature and even at a somewhat 

 higher temperature, and that there are organisms which exist at high temperatures. 

 Obviously these living things have learned to produce proteins which are stable at a high 

 temperatures. 



J. D. Bernal: I only want to touch upon a question raised by Prof. Pauling. The re- 

 arrangement of proteins at the onset of denaturation depends essentially on the length of 

 the chain. Calculations carried out in our Laboratory show that the character of the forces 

 of the bonds in ordinary proteins corresponds well with what is known of the process of 



