SESSION V. DISCUSSION 



499 



One method of investigation, which opens up new possibilities for the study of the 

 structural relationships which enter into the composition of the components of nucleo- 

 protein, is the study of artificial complexes obtained from native preparations of nucleic 

 acid and protein. The study of these is of interest in connection with the findings, which 

 have recently appeared in the literature, concerning the alteration in the biological activity 

 of proteins when they are bound in a complex with nucleic acid and which probably de- 

 pends on the specificity of the unfolding of the protein molecules on the molecule of 

 nucleic acid. Thus, the work of Japanese scientists has shown an activation of the enzyme 

 urease when it is combined with ribonucleic acid. A nimiber of other authors (Klingenberg, 

 Slavik & Smetana; Sorm) have demonstrated the inactivation of various proteases by 

 ribonucleic acid. In the investigations which he has described G. A. Deborin has also 

 demonstrated the inactivation of trypsin by deoxyribonucleic acid (DNA). We have 

 tried to make a comparative study of some of the physicochemical and enzjmiic properties 

 of artificial nucleoproteins made from DNA and a-chymotrypsin, depending on the 

 amount of the latter present in the complex. We made the complexes from highly 

 polymeric DNA (mol. wt. 3-3-5 x lo^), and crystalline a-chymotrypsin, used in a con- 

 centration corresponding with its existence in the monomeric form, in the mild condi- 

 tions under which they were prepared in an insoluble state (pH 4-5) and could be separated 

 in the pure state from the starting materials which had not entered into the reaction. 



500 



400 



300 



200 



100 



D-D, 



Chymolrypsin 



50 



60 70 



Protein^ 



80 



90 



iÖ^ 



Fig. I. Specific proteolytic activity of a-chymotrypsin boimd to DNA depending 

 on the proportion of the former in the complex. 



The compounds obtained had a number of the properties of natural nucleoproteins; 

 they formed fibrillar precipitates in physiological solutions of sodium chloride; they 

 showed the decrease in viscosity characteristic of artificial and natural nucleoproteins, 

 which is caused by a decrease in the asymmetry of the DNA molecule when it combines with 

 protein ; they had the characteristic capacity of nucleoproteins for high-elastic deformation. 



When studying the conditions of formation of the complexes it was found that if the 

 proportion of protein to DNA in the reaction mixture was increased, the amount of protein 

 bound to each molecule of DNA was increased. Thus, by varying the starting proportions 

 of protein and DNA, it was possible to obtain a series of complexes containing different 

 proportions of protein and DNA and to study the dependence of some of their physico- 

 chemical and biological properties on this factor. This aspect of our investigations allowed 

 us to estabUsh interesting, regular associations between the structural-mechanical pro- 

 perties of the complexes (viscosity, relative relaxation) and the amount of protein in them; 

 the results of this part of our study have been shortly described by V. S. Tongur in his 

 communication. 



Studies of the specific proteolytic activity of the chymotrypsin in complexes with 

 different protein contents, varying over a wide range, from 45-92%, were carried out 

 under the same conditions of enzymic concentration (calculated from the protein content 

 of the complex) and relationship of the enzyme to the substrate. 



