198 HUBERT S. LORING 



In the original procedure given by Levene and Jacobs^* for the prepara- 

 tion of guanosine, adenosine, cytidine, and uridine, yeast nucleic acid was 

 heated with concentrated ammonium hydroxide under pressure in an oil 

 bath at 175-180° for 3.5 hours. More recently aqueous pyridine^^ (under 

 reflux for 43^ days), a catalytic hydrolysis with lanthanum,^^ and phos- 

 phatase hydrolysis of nucleotides^^-^" have been used to prepare the purine 

 and pyrimidine ribonucleosides in moderate quantities. Their fractionation 

 by starch chromatography^' in milligram quantities has also been reported. 



h. Formation of Nucleotides 



As mentioned above, the pyrimidine nucleotides were recognized as acid- 

 resistant phosphate hydrolysis products of yeast PNA in 1911.'^ The dis- 

 covery that similar organic phosphate compounds could also be produced 

 during alkaline hydrolysis of yeast PNA was made independently by 

 Thannhauser and Dorfmuller'*^ an(j ^y Jones and Germann*^ when this sub- 

 stance was treated with ammonia under milder conditions (2.3 % NH3 for 

 1 hour at 115°) than those used by Levene and Jacobs^* for the formation of 

 nucleosides. The subsequent purification, isolation, and crystallization of 

 the compounds known as uridylic acid,'^ adenylic acid,'**- '^^ cytidylic acid,'^ 

 and guanylic acid^^ resulted from work performed in the three laboratories 

 mentioned on either ammoniacal hydrolysates of yeast PNA or, for the 

 pyrimidine mononucleotides, on acid hydrolysates. The still milder hydroly- 

 sis with approximately 1 A^ NaOH at room temperature was discovered by 

 Steudel and Peiser^^ in experiments in which guanylic and adenylic acids 

 were isolated from yeast PNA after application of this procedure. More 

 recently 1 N alkali at 37°/ 0.6 N Ba(0H)2 ,^» and 0.1 N NaOH at 100° '' 

 have been used. 



36 H. Bredereck, A. Martini, and F. Richter, Ber. 74, 694 (1941). 



37 F. A. Allen and J. E. Bacher, /. Biol. Chem. 188, 59 (1951). 



38 J. M. Gulland and T. F. Macrae, J. Chem. Soc. 1933, 662. 



39 H. S. Loring, M. L. Hammell, L. W. Levy, and H. W. Bortner, J. Biol. Chem. 196, 

 821 (1952). 



" P. Reichard, Y. Takenaka, and H. S. Loring, J. Biol. Chem. 198, 599 (1952). 



« P. Reichard, Nature 162, 662 (1948) ; /. Biol. Chem. 176, 763 (1949). 



« S. J. Thannhauser, Z. physiol. Chem. 91, 329 (1914); S. J. Thannhauser and G. 

 Dorfmiiller, 95, 259 (1915); 100, 121 (1917). 



" W. Jones and H. C. Germann, J. Biol. Chem. 25, 93 (1916). 



*^ W. Jones and R. P. Kennedy, /. Pharmacol. Exptl. Therap. 12, 253 (1918). 



45 S. J. Thannhauser, Z. phyaiol. Chem. 107, 157 (1919). 



*6 Guanylic acid was named by Bang in Olaf Hammarsten's laboratory [0. Bang, Z. 

 physiol. Chem. 26, 133 (1898-99)] as a hydrolysis product of pancreas. It was dis- 

 covered as a component of yeast RNA and crystallized by Levene [P. A. Levene, 

 J. Biol. Chem. 40, 171 (1919) ; 41, 483 (1920)]. 



" H. Steudel and E. Reiser, Z. physiol. Chem. 114, 201 (1921); 120, 292 (1922). 



« H. S. Loring, P. M. Roll, and J. G. Pierce, J. Biol. Chem. 174, 729 (1948). 



