ISOLATION AND COMPOSITION OF DEOXYPENTOSE NUCLEIC ACIDS 333 



enzyme-resistant portions. [Compare Chapters 11 and 15.] An example of 

 the application of Procedures II and III has been given above in Section 

 III.2.a.(2). IV. Dialysis against, or other treatment with, dilute alkah t^^i'*- 

 143,146 ^i^jg procedure injures, as it purifies, the deoxypentose nucleic acids, 

 though without noticeable change in composition;'^* the pentose nucleic 

 acids are converted quantitatively to mononucleotides."* [Compare Chap- 

 ters 5, 11, and 16.] Examples can, in fact, be found in the literature in which, 

 after the application of a modified Schmidt-Thannhauser procedure,'" the 

 composition of both deoxypentose and pentose nucleic acid was deter- 

 mined in the same cell or cellular fraction. '^*-'^^ V. Preferential adsorption 

 of pentose nucleic acid on activated charcoal:'*" this procedure is very 

 effective, if the preparation has been freed thoroughly of protein and if the 

 deoxypentose nucleic acid, but not the pentose nucleic acid, is highly 

 polymerized, as is usually the case. The adsorbed pentose nucleic acid can 

 be recovered by extraction of the adsorbent with aqueous phenol.'''^ VI. 

 Separation of deoxypentose and pentose nucleic acids by means of cetyl- 

 trimethylammonium bromide. ''•^^ — Procedures I, II, V, and VI permit the 

 recovery of pentose nucleic acid. 



Impurities of low molecular weight are best removed by dialysis against 

 water or, preferably, physiol. saline. The removal of protein has been 

 described before (Sections III.2.a-c?). The elimination of high-molecular 

 contaminants, especially polysaccharides, often is not easy, since the op- 

 portunity of using a specific enzyme^^ will not frequently present itself. 

 Unless recourse is had to the mechanical separation of the fibrous sodium 

 or calcium deoxypentose nucleate from the usually granular polysaccharide 

 — a form of handicraft that often is surprisingly effective — a precipitating 

 agent for nucleic acids, specific within certain limits, may be employed, 

 e.g., lanthanum salts, "^■'*' from which the deoxypentose nucleic acid is 

 recovered as the potassium salt by treatment with potassium oxalate, or 

 such tervalent complex cations as hexammine cobaltic chloride.'*- 



IV. Properties of Deoxypentose Nucleic Acids 



1. Elementary Composition and Standards of Integrity 



Deoxypentose nucleic acids are usually isolated as the sodium salts or, 

 occasionally, as the potassium salts. "^■'*' The sodium nucleate from calf 



" G. Schmidt and S. J. Thannhauser, J. Biol. Chem. 161, 83 (1945). 



^« A. Marshak, J. Biol. Chem. 189, 607 (1951). 



" D. Elson and E. Chargaff, Experientia 8, 143 (1952). 



" D. Elson and E. Chargaff, Phosphorus Metabolism 2, 329 (1952). 



^« D. Elson, T. Gustafson, and E. Chargaff, J. Biol. Chem. 209, 285 (1954). 



«» S. Zamenhof and E. Chargaff, Nature 168, 604 (1951). 



«' E. Vischer, S. Zamenhof, and E. Chargaff, J. Biol. Chem. 177, 429 (1949). 



«2 E. Chargaff and C. Green, J. Biol. Chem. 173, 263 (1948). 



