isolation and composition of pentose nucleic acids 387 



2. Isolation of PNA from Animal Tissues 



Chargaff ct al. isolated PNA from the livers of several species of animals.^* 

 Their procedure was based on a modification of the method of Davidson 

 and Waymouth.-* PNA was dissociated from protein by boiling in 10% 

 NaCl. An analogous procedure used by the same authors for the isolation 

 of PNA from baker's yeast, is described in detail below. Similar methods 

 were used by Tsuboi and Stowell^^ and by Davidson et al}^ for the isolation 

 of PNA from liver, and by Davidson and Smellie for the isolation of PNA 

 from cytoplasmic fractions of the liver/^ 



PNA was prepared from beef pancreas by Kerr and Seraidarian^^ by a 

 method in which the nucleoprotein, isolated by isoelectric precipitation, 

 was dissociated by exposure in a half-saturated solution of NaCl for a 

 period of 36 hours or more. The danger of degradation of PNA during 

 isolation by tissue ribonuclease is particularly great in the preparation of 

 PNA from pancreas. Bacher and Allen described the preparation of PNA 

 from pancreas after removal of ribonuclease by extraction with dilute acid 

 and acetone.^* 



A general method for the preparation of PNA from different animal 

 tissues, including liver, spleen, thymus, and pancreas, was described by 

 Volkin and Carter.^^ It consists of the precipitation of PNA from a cold 

 2 M guanidine hydrochloride solution in which protein remains soluble. 

 Their procedure is described in detail below. A modification of this method 

 was used by Grinnan and Mosher for the preparation of highly polymer- 

 ized PNA from rat and rabbit liver.^^ The nucleotide composition of their 

 preparations was not determined. Recently, the preparation of PNA from 

 liver, pancreas, and tumor tissue by the use of sodium dodecyl sulfate has 

 been described by Kay and Dounce.^^ 



(1) Preparation of Mamvialian Tissue Ribonucleic Acid.-^ The method 

 of isolation of ribonucleic acid from tissue homogenates consisted of (a) 

 the removal of deoxyribonucleic acid as a nucleic acid - protein complex, 

 (b) the precipitation of the ribonucleic acid from a cold 2 M guanidine 

 hydrochloride solution in which the large bulk of protein remains soluble, 

 and (c) further purification of the ribonucleic acid by chloroform extrac- 

 tion and alcohol precipitations. 



The possibility of the occurrence of nuclease action on ribonucleic acid 

 duringlthe preliminary steps of the preparation can be obviated by imme- 



^* E. Chargaff, B. Magasanik, E. Vischer, C. Green, R. Doniger, and D. Elson, 



/. Biol. Chem. 186, 51 (1950). 

 « K. K. Tsuboi and R. E. Stowell, Biochim. et Biophys. Acta 6, 192 (1950). 

 . ^6 J. N. Davidson, S. C. Frazer, and W. C. Hutchinson, Biochem. J. 49, 311 (1951). 

 ■" J. N. Davidson and R. M. S. Smellie, Biochem. J. 52, 600 (1952). 



