NUCLEIC ACIDS 139 



and this in turn could be oxidized to uric acid 



C 5 H 4 N 4 2 +0 = C 5 H 4 N 4 3 



but it would be necessary to introduce the first oxygen atom into position 

 two, and the second, into position eight. While no chemical oxidizing 

 agent has been found that can effect this selective oxidation, oxidizing 

 ferments are present in the tissues that can direct the oxygen atoms into 

 their proper positions, and bring about the conversion of hypoxanthine 

 successively into xanthine and uric acid. 



The converse reactions which involve the withdrawal of oxygen can 

 be effected in the laboratory. Uric acid has been successively reduced to 

 xanthine and hypoxanthine. (Sundwick, 1911.) 



The Nucleotides of Yeast Nucleic Acid. The older investigators 

 knew that by mild acid hydrolysis, nucleic acid is partly split up, setting 

 free part of its phosphoric acid, part of its carbohydrate and all of its 

 purine bases; but that the remainder of its phosphoric acid and carbo- 

 hydrate, together with its pyrimidine compounds, are set free only after 

 most violent methods of hydrolysis. It was therefore natural to assume 

 that nucleic acid is composed of four "complexes," all of which produce 

 both phosphoric acid and carbohydrate, but each "complex" produces a 

 different one of the four nitrogenous compounds. The two purine "com- 

 plexes" evidently undergo hydrolysis with ease, while the two pyrimidine 

 "complexes" are very stable. If the term "nucleotide" be substituted for 

 the term "complex," this becomes essentially the modern nucleotide the- 

 ory of the constitution of nucleic acid. This theory was originally pro- 

 posed on the speculative grounds as outlined above, before any nucleoside 

 or nucleotide had been prepared from nucleic acid; but it has recently 

 received firm experimental support by the preparation from yeast nucleic 

 acid of the four assumed nucleotides 



H0\ 



O=P O.C 5 H 8 O 3 .C 5 H 4 N 5 O 

 HO/ 



Guanine Nucleotide (Jones and Richards, 1914) (Read, 1917) 



HO\ 



0=P O.C 5 H 8 3 .C 4 H 4 N 3 

 HO/ 



Cytosine Nucleotide (Thannhauser and Dorfmiiller (a) (6), 1918, 1919) 



HO\ 



0=P O.C 5 H 8 3 .C 5 H 4 N 5 

 HO/ 



Adenine Nucleotide (Jones and Kennedy, 1918) 



