80 CONJUGATED PROTEINS 



organisms 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 deoxy- 

 nucleoproteins. The bonds holding the ribonucleic acid to the 

 protein are broken with much less ease; and one gains the im- 

 pression 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 nucleohistone may be com- 

 pared 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 a new dimension; but each partner is, in itself, 

 fully competent to maintain a specific pattern and to convey 

 intricate information. 



Of the lipoproteins, on the other hand, it could be said that it 

 is only through the attachment of the monomeric lipids to a 

 protein that a specific pattern of lipid arrangement becomes pos- 

 sible. It is not improbable that the future will show that certain 

 lipids can exist in the cell in a polymerized form capable of 

 exhibiting sequential specificity. But up to the present the lipids 

 seem to be the only bulk components of tissues that must be as- 

 sumed to exist principally in a monomeric form. If the establish- 

 ment of specific arrangements is considered as an attribute of 

 cellular organization, the formation of specific lipoproteins is one 

 of the ways in which the lipids can take part in such specific 

 patterns. Certain lipids probably are attached to the proteins 

 by a combination of electrostatic and hydrogen bonds; others 

 may occur as solutions in the lipid moieties of lipoproteins. 



