KIDNEY AND SKIN AS SECRETORY ORGANS. 



849 



The nucleosides (adenosin and guanosin) may first be converted 

 to the corresponding oxy-compounds (xanthosin and inosin), and 

 then by hydrolysis the carbohydrate is split off with the liberation 

 of xanthin and hypoxanthin. 



4. The xanthin and hypoxanthin, under the influence of an oxi- 

 dase (xanthinoxidase), are in part oxidized to uric acid, C5H4N4O3. 

 In man this oxidase seems to occur only in the liver, so that the 

 immediate production of uric acid must be referred to this organ. 



5. In man the uric acid, xanthin, and hypoxanthin represent 

 the final end-products of the metabolism of the nucleic acid or, 

 rather, of the purin nucleotide portion of its molecule, and to 

 the extent that they occur in the urine they indicate so much 

 nucleic acid broken down. In the other mammals the oxidation 

 process goes a step further — the uric acid is converted to allantoin 

 by an oxidase known as uricolytic enzyme or uricase, whose action 

 may be represented by the equation : 



C6H4N4O3 + H2O + O = C4H6N4O3 + CO2 



Uric acid. Allantoin. 



These changes may be represented by the following diagram 

 (Jones) : 



Nucleic acid. 



Hypoxanthia. 



Origin and Significance of the Creatinin and Creatin. — 



Creatinin (C4H7N3O) occurs in the urine, and it was formerly as- 

 sumed that it is derived from the creatin (C4H9N3O2) found in 



/NH - CO 

 muscle. Its structural formula is given as NHC<' | and its 



\n(CH3)CH2 

 chemical relations are indicated by the fact that it may be prepared 

 synthetically from methyl-glycocoU and cyanamid — that is, the 

 union of these two substances gives creatin, from which in turn 

 creatinin may be obtained by loss of a molecule of water. 

 54 



