ISOLATION AND COMPOSITION OF DEOXYPENTOSE NUCLEIC ACIDS 309 



but when the direction of the quest became reasonably well defined, the 

 results sharpened in definition. Though we still are very far from a solution 

 of the many problems that keep multiplying as our knowledge progresses, it 

 would be hazardous to erect a sign saying "Ignorabimus." But much is left 

 to future generations. 



The deoxypentose nucleic acids have often been isolated by way of the 

 nucleoproteins. That the use of these conjugated proteins also has provided 

 an encouraging procedure for nucleic acid fractionation will be mentioned 

 later. In other cases direct isolation methods for the preparation of the 

 nucleic acids from a variety of tissues have been employed. These different 

 procedures will be described after a brief consideration of the nucleopro- 

 teins themselves. These sections will in turn be followed by a discussion of 

 the properties and of the composition, in both its qualitative and quantita- 

 tive aspects, of the deoxypentose nucleic acids. Their fractionation and 

 methods for their structural investigation will betaken up next; and, finally, 

 a provisional summation will be attempted. 



II. Deoxypentose Nucleoproteins 



1. General 



Beneath the simple textbook definition of a nucleoprotein^ — a combina- 

 tion between a protein and a nucleic acid — there lies an ocean of uncertain- 

 ties. Studies on nucleoproteins lead right into one of the most neglected, 

 because most difficult, fields of present-day biochemistry, namely, the con- 

 jugated proteins. The deoxynucleoproteins are usually defined as conjugated 

 proteins in which the union between the deoxypentose nucleic acid, func- 

 tioning as a prosthetic group, and the protein is mediated by electrostatic 

 attraction or by secondary valence forces.®"* It is, however, as was pointed 

 out some years ago in a discussion of the cognate problem of the lipopro- 

 teins,^ extremely difficult to distinguish between these two types of combina- 

 tion when dealing with macromolecules. Moreover, a decision will have to 

 be made in every case whether what has been isolated really preexisted in 

 the cell as a conjugated protein or whether it was produced by the com- 

 bination between solutes fortuitously present in the same cell extract, thus 

 simulating a definite compound. One of the attributes of a conjugated pro- 

 tein is that it must differ in some of its properties from a mere mixture of 

 its components. A genuine nucleoprotein would, therefore, have to be re- 

 garded as a geometrically unique compound between two giant polyampho- 



* J. P. Greenstein, Advances in Protein Chem. 1, 209 (1944). 



^ E. Chargaff, Cold Spring Harbor Symposia Quant. Biol. 12, 28 (1947). 



8 E. Chargaff, in "Some Conjugated Proteins," p. 36. Rutgers University Press, 



• New Brunswick, New Jersey, 1953. 



' E. Chargaff, Advances in Protein Chem. 1, 1 (1944). 



