42 DEOXYPENTOSE NUCLEOPROTEINS AND PROSTHETIC GROUPS 



nucleohistones mostly investigated in the form of calf thymus 

 nucleohistone; (3) the nucleoproteins in the proper sense of this 

 term in which the nucleic acid is combined with a protein lacking 

 the basic properties of the protamines and histones^. We are, 

 however, very far from a satisfactory classification of the types 

 of deoxynucleoprotein occurring in cell nuclei, especially with 

 regard to changes in the composition of the protein moiety taking 

 place during development and in the various phases of the mitotic 

 cycle. 



b. Isolation 



The principal methods for the preparation of nucleoprota- 

 mines and nucleohistones, i.e., complexes in which the protein 

 partner carries a positive charge, are based on (a) extraction with 

 strong salt solutions^; (b) extraction with solutions of low ionic 

 strength^^. The first-mentioned procedure, widely used as the 

 first step in the isolation of deoxypentose nucleic acids, is ac- 

 companied by an, at least partial, dissociation and may lead to 

 artifacts. It has, on the other hand, the advantage that the activity 

 of deoxyribonucleases is suppressed in strong salt solutions. By 

 extraction with solutions of low ionic strength the exposure of 

 the conjugated protein to dissociating conditions in the course of 

 its preparation is avoided. There exists, however, the danger of 

 a partial enzymic degradation of the nucleic acid brought about 

 by the release of nucleases. As examples of the isolation of 

 nucleohistone at a low electrolyte concentration the studies on 

 calf thymus nucleohistone in Refs. 4 and 11 may be cited; the 

 isolation of a nucleoprotamine from sea-urchin sperm is discussed 

 in Ref. 12. Preparations afforded by extraction with strong 

 salt solutions are described, for instance, in Ref. 13. The isolation 

 from avian tubercle bacilli of a nucleoprotein with entirely dif- 

 ferent solubility properties has been reported^. 



c. Properties 



A real decision on the native state or the attributes of intact- 

 ness of a nucleoprotein will hardly be possible before suitable 



