ISOLATION AND COMPOSITION OF DEOXYPENTOSE NUCLEIC ACIDS 319 



b. Cleavage and Degradation 



It already has been mentioned (Section 11.3. b) that there exists con- 

 siderable evidence that deoxypentose nucleoproteins, or at any rate the 

 nucleoprotamines and nucleohistones, occur in strong salt solutions in a 

 largely dissociated state which has often been regarded as representing no 

 more than a mixture of protein and nucleic acid. This cleaving effect of a 

 high concentration of salt" has been employed in what, historically speak- 

 ing, is one of the most important procedures for the isolation of intact 

 deoxypentose nucleic acid, namely, that of Hammarsten.^" It is also demon- 

 strated by the observation that the nucleic acid can be freed entirely of 

 protamine by the dialysis of the nucleoprotamine of trout sperm in the 

 presence of M NaCl." The addition of alcohol to a salt solution of nucleo- 

 histone has a similar effect.^" '^'^ The fractional dissociation of nucleohistone 

 by increasing concentrations of salt has been studied in some detail by 

 Crampton et al.^" They discuss the possibility that even at a high ionic 

 strength there may remain some residual unbroken links between the 

 nucleic acid and the histone unless one of the partners is being removed 

 continually. 



While agents known to break hydrogen bonds, e.g., urea, guanidine, etc., 

 do not seem to have been much employed for preparatory purposes, the 

 detergents have found useful application. After the discovery of the effect 

 of sodium dodecyl sulfate on tobacco mosaic virus," this substance or 

 similar commercial detergent preparations often have served for the isola- 

 tion of deoxypentose nucleic acid. (See below. Section III.2.C?.) Sodium 

 deoxycholate has also been used occasionally.^''^* 



The degradation of deoxypentose nucleoproteins has, in contrast to their 

 cleavage, been little studied, no doubt because of their lability and unfavor- 

 able solubility properties. Here again, though title or text may not indicate 

 it, much of the work probably deals with the nucleic acids rather than with 

 the nucleoproteins. Nemchinskaya^^ found depolymerization to be retarded 

 when pancreatic deoxyribonuclease acted on a nucleoprotein. 



c. Artifacts 



It is very easy to mix a nucleic acid with a protein, but very difficult 

 to describe the resulting product. The childish urge to pour all into one pot 

 has abated of late and the term nucleoprotein is no longer applied to every 

 concoction. This has been brought about by a realization of the enormous 



" M. Sreenivasaya and N. W. Pirie, Biochem. J. 32, 1707 (1938). 



'« O. T. Avery, C. M. MacLeod, and M. McCarty, J. Ezptl. Med. 79, 137 (1944). 



"* V. L. Nemchinskaya, Biokhimiya 15, 478 (1950); Chem. Abstr. 45, 3439 (1951). 



