SESSION VI. DISCUSSION 581 



autocatalytic reactions discussed by Calvin, reactions are also reinforced by the inter- 

 weaving of the catalytic or activizing effects of the products. 



Thus, on the one hand, nucleic acids subserve the process of protein synthesis, while, 

 on the other, proteins, in the form of the appropriate enzymes, catalyse the biosynthesis 

 of nucleic acids. 



Another example. The biosynthesis of nucleotides from their simple precursors leads 

 to the formation of nucleotide coenzymes which take part in glycolytic and oxidative pro- 

 cesses. On the other hand, as a result of glycolytic and oxidative processes, ribose-5- 

 phosphate and pyrophosphate are formed and these take part in the biosjmthesis of nucleo- 

 tides from their simpler precursors. 



2. In trying to find out the path of biosynthesis of proteins it would seem to be useful 

 to take note of some analogies, namely those with the biosynthesis of polysaccharides and 

 nucleic acids. It is well known that the synthesis of polysaccharides and nucleic acids is 

 brought about by reversible reactions of phosphorolysis or pyrophosphorolysis. The 

 reversible reactions of phosphorolysis of glycogen or pyrophosphorolysis of deoxy- 

 ribonucleic acid may only lead to a lengthening of the already existing chain of the poly- 

 mers (primers). An actual increase in the number of molecules of a polymer can obviously 

 occur owing to the presence of a certain amount of hydrolytic enzymes which, in an orderly 

 way and to a limited extent, divide up the extremely large molecules of the original polymer 

 into a few smaller ones. With some changes, such a state of affairs may also occur in the 

 process of the biosynthesis of proteins. As an example, we may take the formation, studied 



Original polymer 



'Primer' ^^ ^^/~N Secondary 



:- ■ u ^-^ 3 Vv polymers 



Energy-nch ^ ^-^ '^ -' 



monomer 



Fig. I. General scheme of the biosynthesis of glycogen, ribonucleic acid, 

 deoxyribonucleic acid and protein. 



The process of formation of the original poljrmer takes place with the help 

 of the 'primer' and with an increase in free energy, ( + AE), while the process 

 of breakdown of the original polymer into secondary polymers takes place without 

 a 'primer' and with a decrease in free energy (— A£). 



1. Retrophosphorolysis, retropyrophosphorolysis and other reactions of 

 polymerization. 



2. Partial hydrolysis. 



3. The dotted line indicates that one of the products of the breakdown may 

 be able to act as a 'primer'. 



The enrichment of amino acids with energy in the biosynthesis of protein 

 may occur by coupling of the carboxyl groups of amino acids with the phosphate 

 groups of nucleotides. 



by Northrop, of active proteolytic enzymes in the aUmentary tract of animals from pro- 

 enzymes by the proteolytic splitting of the proenzyme into the enzyme and an inactive 

 polypeptide. The protein which is present on the surface of the nucleic acid might be the 

 original high polymer. 



It would seem that only one experimental fact contradicted this scheme, namely the 

 fact that, according to the published evidence, the reaction of 'retrophosphorolysis' of 

 ribonucleic acid takes place without a primer. However, as we showed about 10 years ago, 

 it would appear that all preparations of native proteins and enzymes have in their com- 

 position (perhaps in the form af adsorbed impurities) a nucleotide or nucleic acid pros- 

 thetic group which could obviously serve, in this case, as a 'primer'. 



