852 PHYSIOLOGY OF DIGESTION AND SECRETION. 



wholly agreed upon by the different workers. It is supposed that 

 the nucleic acid is liberated from its combination with protein by 

 the action of the known proteolytic enzymes, such as pepsin or 

 trypsin or the similar autolytic enzymes in the tissues. For the 

 destruction of the nucleic acid itself there is a series of special 

 enzymes whose action as described by Jones is essentially as follows : 



1. The tetranucleotide is split into two dinucleotides (purin and 

 pyrimidin) by the enzyme tetranuclease. The further history of 

 the pyrimidin nucleotides is not known. 



2. The purin nucleotides are split by two enzymes, phospho- 

 nuclease and purin-nuclease. The former splits off phosphoric 

 acid and leaves the purin bases in combination with the carbo- 

 hydrate, giving two compounds known as nucleosides, namely, 

 adenosin and guanosin. The purin-nuclease splits off adenin and 

 guanin in free form . 



3. The four substances, adenin, guanin, adenosin, and guanosin, 

 are acted upon by corresponding deaminizing enzymes, adenase, 

 guanase, adenosin-deaminase, and guanosin-deaminase, and con- 

 verted to oxypurins. For the adenin and guanin the reaction is as 

 follows : 



C 5 H 5 N 5 + H 2 O = C 6 H4N 4 O + NH 3 



Adenin. Hypoxanthin. 



H 2 O = C 5 H 4 N 4 O 2 + NH 3 



Guanin. Xanthin. 



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, CsH^N^s. 

 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 : 



4O 3 + H 2 O + O = C 4 H 6 N 4 O 3 + CO 2 



Uric acid. Allantoin. 



Origin and Significance of the Creatinin and Creatin. 



Creatinin (C^yNaO) occurs in the urine, and it was formerly as- 



