THE NUCLEIC ACIDS 



with the highest possible precision in the absorption measurement it is 

 not possible to make an exact determination of the amount or character 

 of the proteins.' There is some doubt whether the absorption spectrum 

 of a mixture of protein and nucleic acid is entirely the sum of that of 

 each component. Ferkhmin'^^ claims to have shown that those of 

 adenylic acid and tyrosine are non-additive; I have been informed by 

 Bracket that the same is true of nucleic acid in the presence of the 

 protein edestin. It is here of interest that Rudall^" reports that in the 

 x-ray diffraction pattern of 'the fibrous product of combination be- 

 tween nucleic acid and edestin . . . neither nucleic acid structure nor 

 protein structure can be recognized'. If interaction between proteins 

 and nucleic acids, or between their constituent units may influence 

 their ultraviolet absorption, microspectrometric measurements on cells 

 will be affected by the extent to which these constituent substances are 

 combined within the specimen under test. It is generally believed the 

 linkage between nucleic acids and proteins is destroyed when tissues 

 are fixed; it would be highly desirable to know whether this is always 

 wholly true of dead cells, even when the freeze-drying technique has 

 been used. Such technical matters relating to the validity of micro- 

 spectrometric research methods may well be of greater importance to 

 those which have recently been raised on optical grounds (Gom- 

 MONER^i). They are peculiarly relevant to the question of the relation- 

 ship between protein synthesis and the nucleic acids, the evidence for 

 which we shall now attempt to discuss. 



NUCLEIC ACIDS AND PROTEIN SYNTHESIS 



The general thesis that nucleic acid is abundant in cells which are 

 synthesizing proteins at a comparatively rapid rate is due both to 

 Caspersson'2 ^2 and to Brachet,^^ who were working simultaneously 

 by different methods, and came independently to the same conclusion. 

 Bracket used the Unna-Pappenheim staining technique, and studied 

 the effect of ribonuclease on the basophilia towards the pyronin 

 component of this mixture. Instances of cells and tissues in which both 

 workers have observed this correlation of nucleic acid content and 

 synthetic activity are the exocrine glands, keratinizing epithelia, 

 embryonic tissues in which mitosis is frequent and also the developing 

 oocyte. The neurone was also included in this scheme when it was 

 realized (Hyden^^) that here also proteins are produced and are used 

 up during functional activity. A further example is that of the silk 

 glands of the Arachnida (Bradfield^^), and the available evidence is 

 by no means confined to the cells of Metazoa (Davidson^^) . 



The accumulation of nucleic acids within the cells of a tissue may 

 anticipate growth and protein production (Caspersson^^). In tumour 



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