734 URINE. 



to BRION x ; thus in dogs the levotartaric acid is almost entirely consumed, 

 while a little more than 70 per cent of dextrotartaric acid is burnt. Race- 

 mic acid is oxidized to a still less extent in the animal body. Succinic 

 and malic acids are completely combustible, according to PoHL. 2 Ex- 

 amples of the different behavior of stereoisomeric substances have already 

 been given on page 199. 



The acid amides do not appear to be altered in the body (SCHULTZEN and 

 NENCKI 3 ) . The amino-acids may, indeed, when introduced into the body 

 in large quantities, be in part eliminated unchanged by the urine; but 

 otherwise, as stated above (page 648) for leucine, qlycocoll, and aspartic 

 acid, they are decomposed within the body, and may therefore cause an 

 increased excretion of urea. That in the demolition of the amino-acids 

 a deamidation takes place is shown by alanine yielding lactic acid and 

 diaminopropionic acid, yielding gly eerie acid, as mentioned in a previous 

 chapter (VIII). The amino-acids give an instructive example of the 

 unequal behavior of stereometric substances in the animal body, as the 

 racemic acids are so changed and transformed that the component foreign 

 to the body is burnt with more or less difficulty, while the component 

 occurring in the body protein is burnt, on the contrary, with ease and 

 more completely . ABDERHALDEN 4 and his collaborators have shown that 

 the polypeptides when introduced into the body are decomposed with 

 the formation of urea similar to the amino-acids, and this probably occurs 

 by a previous decomposition into their simplest fractions, the amino- 

 acids. 



We do not know exactly how the amino-acids are split in the animal body. 

 DAKIN has shown that in the oxidation of the amino-acids by hydrogen peroxide 

 outside of the body under certain conditions the reaction proceeds with the 

 formation of ammonia, carbon dioxide and an aldehyde, which latter is then further 

 oxidized with the formation of the corresponding acid and other products. 

 For example, leucine first yielded isovaleric aldehyde, then isovaleric acid, 

 (CH 3 ) 2 .CH.CH 2 .COOH, from which, DAKIN claims, acetone is derived (see under 

 acetone bodies, page 774), with /3-oxyisovaleric acid, (CH 3 ) 2 .C(OH).CH 2 .COOH, 

 probably as intermediary step. In a series of investigations DAKIN 5 calls atten- 

 tion to the correspondence which exists between the artificial oxidations and 

 several known decompositions in the animal body, which indicate a similar 

 decomposition of amino-acids in the living organism. According to NEUBAUER" 

 the destruction of the amino-acids occurs, in that the corresponding keto acid, 

 R.CO.COOH is first formed by an oxidative deamidization, and not, as generally 

 admitted, the corresponding oxyacid. The keto acids are by oxidation with the 

 splitting off of CO 2 then transformed into the next lower fatty acid. 



1 Zeitschr. f. physiol. Chem., 25. 



2 Pohl, Arch. f. exp. Path. u. Pharm., 37, which also contains reports on the 

 intermediary products formed in the oxidation of the fatty bodies. 



3 Zeitschr. f. Biol., 8. 



4 Zeitschr. f. physiol. Chem., 39, 46, 47, 48, 52, 55, 57. 



5 Dakin's work can be found in Journ. of biol. Chem., 1, 2, 3, 4. 



6 Cited in Physiol. Centralbl., 23, 76. 



