192 HUBERT S. LORING 



acid, however, that the purine riboside or deoxy riboside linkage is unusu- 

 ally labile to acid hydrolysis, while the pyrimidine riboside or deoxyribo- 

 side linkage is relatively resistant. Similarly, phosphate ester groups 

 attached to purine nucleosides in the 2'- or 3'-positions are relatively acid- 

 labile in contrast to those attached to pyrimidine nucleosides. The free pur- 

 ine bases, adenine and guanine, are readily formed during acid hydroly- 

 sis of both types of nucleic acids, whereas the pyrimidine bases remain for 

 the most part as mononucleotides in the case of PNA or as nucleoside di- 

 phosphates in the case of DNA. As the purine bases are cleaved, reducing 

 groups from the A^- riboside or A^'-deoxy riboside linkages are liberated and, 

 depending oil the conditions used, free ribose or deoxy ribose may be 

 formed. 



The two types of nucleic acids show, however, a characteristically dif- 

 ferent behavior in alkali. [Cf. Chapters 10 to 12.] Pentose nucleic acids are 

 split to mononucleotides by treatment in 1 A^ alkali at room temperature 

 in contrast to DNA which is little affected, as far as precipitability by tri- 

 chloroacetic acid is concerned, by such treatment. Such procedures have 

 served, therefore, for the fractionation and estimation of the relative 

 amounts of DNA and PNA in tissues.^- ^ [Cf. Leslie, Chapter 16.] 



1. Acid Hydrolysis of PNA 

 a. Liberation of Purine Bases and Ribose 



Acid hydrolysis has often been used in estimating the relative amounts of 

 adenine and guanine, reducing sugar, labile phosphate, and pyrimidine 

 nucleotides in PNA. It is of value, in using such procedures to estimate the 

 amounts of the respective components in different PNA's, to assess the de- 

 gree to which such procedures lead to a quantitative conversion to the 

 respective products. 



The purine bases are liberated from PNA by treatment with alcoholic 

 HCP- 4 or by hydrolysis with 0.4 N,\N,2N,orQN HCl or H2SO4 at 

 100-120° for 1-2 hours.*"* Both types of procedures have been used for the 

 preparation of adenine and guanine from yeast PNA' • ^^"^ as well as in an- 

 alytical procedures for the estimation of purine and pyrimidine componelits. 



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



2 E. Hammarsten, Acta Med. Scand. Suppl. 196, 634 (1947). 



3 P. A. Levene, J. Biol. Chem. 53, 441 (1922). 



* E. Vischer and E. Chargaflf, J. Biol. Chem. 176, 715 (1948). 



« R. D. Hotchkiss, /. Biol. Chem. 175, 315 (1948). 



« S. E. Kerr, K. Seraidarian, and M. Wargon, /. Biol. Chem. 181, 761, 773 (1949). 



7 J. D.' Smith and R. Markham, Biochem. J. 46, 509 (1950). 



8 H. S. Loring, J. L. Fairley, and H. L. Seagran, J. Biol. Chem. 197, 823 (1952). 



9 W. Jones, "Nucleic Acids," 2nd ed. Longmans Green & Co., New York, 1920: (a) 

 p. 107; (b) pp. 41,44. 



