74 Essays in Biochemistry 



As concerns the nucleoproteins, a strict distinction must be made 

 between the complexes containing deoxypentose nucleic acids and those 

 in which a pentose nucleic acid acts as the prosthetic group. When 

 the conjugated proteins associated with the same type of nucleic acid 

 are compared, it will be noticed that their properties are governed by 

 the type of protein they contain rather than by the composition of 

 their nucleic acid moiety. This is undoubtedly due to the ability of 

 proteins to differ much more from each other in their chemical and 

 physical properties than do the nucleic acids. The deoxynucleoproteins 

 are, in many cases, complexes whose protein moiety is represented 

 by a protein of markedly basic properties, such as a histone or a 

 protamine. Although it is inviting to consider such compounds as salts 

 between the cationic protein and the anionic nucleic acid, this would 

 be wrong. It is, for the moment at any rate, much safer to regard the 

 nucleoprotamines and the nucleohistones as specifically conjoined com- 

 plexes of a complicated and, thus far, little-understood geometry to 

 which both electrostatic and secondary valence bonds contribute. 

 What all these compounds, however, appear to have in common is that 

 they are readily dissociated by high electrolyte concentrations and 

 that under conditions permitting the removal of the protein moiety, 

 by precipitation or denaturation, the nucleic acids are liberated. 



Occasionally deoxynucleoproteins are encountered in microorganisms 

 that are exceptional in resembling the ordinary pentose nucleoproteins 

 rather than the nucleohistones. On the other hand, certain plant 

 viruses represent exceptions to the behavior of the most commonly 

 found pentose nucleoproteins. Of the latter, as they occur in the 

 microsomes and the nucleoli, it may be said that they exhibit less of 

 an electrostatic character than the deoxynucleoproteins. The bonds 

 holding the ribonucleic acid to the protein are broken with much less 

 ease; and one gains the impression that in this case the structure of 

 the prosthetic group is inextricably associated with the structure of 

 the entire conjugated protein. Whereas the dissociation of a nucleo- 

 histone may be compared to the removal of branches from the trunk 

 of a tree, the separation of the ribonucleic acid and protein moieties 

 of a ribonucleoprotein resembles much more the disentanglement of 

 the warp and the woof of a fabric. 



All nucleoproteins share, however, one important feature: they are 

 combinations of two types of giant ampholytes, each of which can, 

 and undoubtedly does, exhibit innumerable specificities as regards 

 shape and constituent sequence. Their combination probably does add 



