376 SESSION IV. DISCUSSION 



essential, residual protein which is disposed around the DNA in the fully extended form 

 in the //-configuration and in complete steric correspondence with the DNA. 



We went on to formulate an equation for the greatest amounts of various proteins which 

 can enter into a complex with DNA and which have different molecular weights and dif- 

 ferent numbers of basic groups. This equation shows that, for DNA of a given molecular 

 weight, the molar ratio between the amounts of DNA and protein entering into the complex 

 depends strictly on the molecular weight of the protein. The amount of bound protein 

 is inversely proportional to its molecular weight. The ratio of the weights of protein and 

 DNA entering into the complex remains constant for different proteins. Thus, for example, 

 DNA from both Uver and pancreas (having a molecular weight of the order of 5 x lo"), 

 can bind up to 1000 molecules of serum albumin or up to 3000 molecules of a-chymo- 

 trypsin. This indicates that, in the formation of DNP, a great part is played, not only by 

 salt and other linkages, but also by the ratio of the sizes of the reacting molecules. 



As our calculations show, the maximum number of protein molecules which can be 

 linked with DNA experimentally carmot be arranged around the latter either in the native 

 or in the fully extended form. Calculations on the asymmetry of molecules of DNP 

 contradict the supposition that the molecules of protein are arranged perpendicularly to 

 the axis of the molecules of DNA and our experiments on the viscosity and relaxation of 

 DNP exclude the possibility that, in such a case, multiple layers of protein may be formed 

 on the molecule of DNA. On the otlier hand, the continual diminution of the magnitude 

 of the relaxation of DNP as the amount of protein in it is increased suggests the gradual 

 blocking of the 'centres' in the molecule of DNP which are responsible for its highly 

 elastic properties. Thus, experiment shows that when 900-1000 molecules of serum albu- 

 min are combined with each molecule of DNA the relaxation of the artificial complex is o, 

 while the viscosity with this amovmt of protein does not differ from that in DNP contain- 

 ing only 300-400 molecules of protein per molecule of DNA. This forces us to assume 

 that the greater number of the protein molecules are directly attached to the DNA even 

 if only by part of their surfaces. 



Study of the relaxational properties of nucleoproteins in relation to the amount of 

 protein present in them has shown that these properties appear when there is about 60% 

 of protein in the DNP. It must be supposed that, in this case, owing to interweaving of 

 submolecular structures, there arises the possibility of the formation of what we might call 

 structures of the fourth order. This does not exclude the possibility of relaxation of indi- 

 vidual molecules of DNP. 



Thus, we arrive at the conclusion that DNP shows two points of inversion, the first 

 when the protein content is i5-25°o, which corresponds with the appearance of the 

 true molecule of DNP with its specific tertiary structure and elasticity ; the second when 

 the protein content is 6o°o3 which corresponds (within fairly wide limits of concentration) 

 to the quaternary structure of DNP, with its characteristic structvural-mechanical 

 properties. 



In conclusion, it must be noted that, when the DNA is carrying less than the maximal 

 load of protein, a part of its surface remains free and can, therefore, take part fn specific 

 biochemical reactions, i.e. a nucleoprotein can 'work' as a protein, as DNA and as a 

 nucleoprotein. 



S. E. Bresler (U.S.S.R.): 



The astonishing advances in biochemistry over the past five years enable us to make an 

 experimental approach to the problem of the chemical mechanism of protein synthesis. 

 It is now generally accepted that the synthesis of protein takes place on a template of 

 ribonucleic acid (RNA). The latest results of Fraenkel-Conrat and Schramm make this 

 conclusion almost inescapable. On the other hand it is extremely probable that the energy 

 required for this synthesis is obtained in the form of the chemical energy of macroergic 

 groups, for example the pyrophosphate groups of adenosine triphosphate (ATP). In the 

 experiments of Straub, Khesin, Anfinsen and others ATP itself serves as the donor of 

 energy for the synthesis. Finally, very recently indeed, Hoagland, Zamccnik and their 

 colleagues have identified chemically labile intermediate compounds, namely anhydrides 

 of amino acids with adenylic acid. They are formed from the amino acids and ATP under 

 the influence of a specific enzyme and mineral pyrophosphate is split oflf at the time of 

 their formation. 



