SESSION V. DISCUSSION 493 



complexes of nucleic acids and proteins, the nature of the bond between the components 

 is somewhat different from that in nucleoproteins, e.g. those of viruses. We have made 

 observations on the formation of soluble complexes of deoxyribonucleic acid and serum 

 albumin at pH 5- 1-6-2 with media of various ionic strengths and with various relation- 

 ships and concentrations of the components. It was found, in this way, that the molecular 

 weight, size and shape of the complex formed was very strongly dependent on the condi- 

 tions mentioned. Some of the properties of these complexes suggest that salt bonds are 

 formed in them between the negative phosphate groups of the nucleate and the positive 

 groups of the protein. It is, however, well known that natural nucleoproteins, such as 

 those of viruses, are stable over a considerably greater range of pH and ionic strength 

 of the mediimi. Thus, we may suppose that, in natural nucleoproteins, the protein com- 

 ponent has a spatial configuration such that it permits the formation, not only of salt 

 bonds, but also of hydrogen and covalent bonds. The question arises as to which are the 

 groups of the protein and nucleic acid between which covalent bonds can be formed in 

 such cases. Measurements of the ultraviolet absorption of tobacco mosaic virus and 

 other naturally occurring nucleoproteins showed that the purines and pyrimidines of 

 nucleic acids do not take part in the binding of protein. It is, therefore, most likely that 

 the covalent bonds in naturally occurring nucleoproteins are formed between the amino 

 groups of the protein and the phosphate groups of the nucleic acids. It seems to me that 

 the solution of the problem of the nature of the bond between nucleic acid and protein 

 is necessary for an understanding of the mechanism of the production of nucleoproteins 

 and also of their biological activity and specificity. 



T. N. EvREiNOVA (U.S.S.R.): 



Coacervates 



More than 20 years ago Bungenberg de Jong worked out the theory of coacervation and 

 demonstrated the extensive prevalence of the phenomenon in Uving nature. At present 

 it is the accepted view that the structure of protoplasm is coacervate-like. 



According to the hypothesis worked out by A. I. Oparin, coacervate drops could have 

 been one of the forms in which life originated on the Earth [i]. Coacervates are formed 

 in both hydrophilic and hydrophobic colloidal solutions. Coacervate drops may be ob- 

 tained from inorganic compounds, from sodium silicate and alcohoUc ammonia, from 

 complex salts of cobalt and also from organic substances, poljrvinyl derivatives, acetyl- 

 cellulose in chloroform, carbohydrates, proteins, lipids, nucleic acids and so forth [2]. 



The present communication deals with: (i) The determination of the amount of nucleic 

 acids and their derivatives in coacervate drops and also the question, (2) the formation of 

 coacervate drops, not only from solutions but also from colloidal precipitates. 



I. When looked at with the ultraviolet microscope (E. M. Brumberg) with a luminescent 

 screen, coacervate droplets containing ribonucleic and deoxyribonucleic acids, and also 

 purine and pyrimidine bases, appeared red. The appearance of these drops is shown in 

 Fig. I. 



If the equiUbrium liquid surrounding the drops also contains the above-mentioned 

 compounds, e.g. nucleic acid, the background of the field of vision is also coloured. 



Thus, without any complicated chemical determinations, a single observation serves 

 to decide the question of the distribution of substances absorbing ultraviolet light between 

 the coacervate drops and the equilibrium liquid. Photographs of coacervate drops con- 

 taining nucleic acid taken by ultraviolet and visible light are given in Figs. 2 and 3. 



The quantitative determination of nucleic acid in a single coacervate droplet has been 

 carried out by means of the ultraviolet microscope and photospectral quartz stage of 

 S. A. Gershgorin. The work was done in collaboration with N. V. Korolev. To measure 

 the concentration of nucleic acid, spectral analyses were made of the radiations passing 

 through coacervate drops, some of which contained nucleic acids while others did not, 

 and also through solutions containing known concentrations of the sodium salt of the 

 nucleic acid. 



The spectrograms obtained on the photographic plates were submitted to photometry 

 and the nucleic acid content was then calculated from a fairly simple formula [3]. 



