454 LECTURE XIX. 



in a quite similar manner. Here, evidently, first of all the NH 2 group is 

 removed by the action of a hydrolytic ferment, and then combustion takes 

 place. 



The fact that we are now getting closer to the realization of the actual 

 conditions is shown by the recent investigations of Embden, Salomon, and 

 Schmidt. 1 They conducted through the liver of a dog, right after killing 

 it, blood to which the different amino acids had been added, and found, 

 for example, that leucine caused a considerable increase of acetone in the 

 circulation. Shortly previous it was established by Embden and Kal- 

 berlah 2 that the liver normally produced acetone. Now all of the amino 

 acids do not yield acetone. Thus, for example, it is not formed from 

 aminovaleric acid, although a glance at the formulas of these two acids 

 shows they are closely related compounds: 



CH 3 CH 3 CH 3 CH 3 



\ / \/ 



(r) CH (/?) CH 



(/?) CH 2 (a) CH . NH 2 



(a) CH . NH 2 COOH 



COOH 



Leucine Aminoisovaleric acid 



Perhaps the different behavior of these two amino acids gives us an 

 indication as to the manner in which at least a part of the decomposition 

 products of albumin is acted upon in the tissues. Embden recalled the 

 observation of Knoop 3 that aromatic fatty acids were decomposed in the 

 animal body first, so that there was a cleavage in the side-chain between 

 the a and /? carbon atoms. Thus phenylbutyric acid was first changed 

 into phenylacetic acid. The latter then appeared as phenaceturic acid in 

 the urine. It is perfectly possible that the breaking down of the aliphatic 

 fatty acids takes place in the same way. Thus in the above instance we 

 can imagine that the leucine and aminovaleric acid were first of all robbed 

 of the amino group. From the former isobutylacetic acid is formed, and 

 from the latter isovaleric acid. Then, by loss of carboxyl and oxidation, 

 iso valeric acid is formed from the isobutylacetic acid, and isobutyric 

 acid from the isovaleric acid. Next cleavage takes place between the a 

 and /? carbon atoms. Now if these ideas are correct, we must expect that 



1 Hofmeister's Beitrage, 8, Heft 3/4 (1906). 



2 Ibid. 



3 Der Abbau aromatischer Fettsauren im Tierkorper. Habil.-Schrift, Freiburg i. B. 



1904. 



