AMIDO-ACIDS FORMED IN TRYPTIC DIGESTION. 42 1 



formula C 10 H 15 N 3 5 . This substance gives a similar biuret reaction to that 

 given by antipeptone ; like it also, it does not give Millon's reaction, is very 

 hygroscopic, and, on decomposition with hydrochloric acid, forms lysine and 

 lysatinine, but not tyrosine. It has also been obtained directly from the pro- 

 ducts of advanced tryptic digestion ; it has been found in milk, and in traces 

 in the urine. It is easily soluble in water ; sparingly in cold, more so in hot 

 alcohol, from which it crystallises in microscopic crystals. It is also soluble in 

 carbolic acid and glacial acetic acid, but is decomposed by these solvents, 

 especially at a high temperature. It combines with hydrochloric acid and with 

 phosphoric acid (Phosphorneischsaure). The compound with phosphoric acid 

 is the form in which it naturally occurs in the organism. Sjoqvist 1 has 

 recently estimated the molecular weight of antipeptone by cryoscopic determina- 

 tion at 250 ; this agrees very closely with the molecular weight similarly 

 determined by Siegfried for his new acid, and increases the probability that 

 the two substances are identical. 



When a proteid is subjected to tryptic digestion, a portion is decomposed 

 beyond the stage of albumose or peptone, and there are formed several nitro- 

 genous bodies of much simpler constitution ; of these, some are amido-acids 

 and some organic bases. Of these substances, two amido-acids, leucine or amido- 

 caproic acid, and tyrosine or para-oxyphenylamido-propionic acid, are present in 

 much larger quantity than the others, which only occur in traces. These others 

 are aspartic acid or amido-succinic acid, glutamic acid or amido-pyrotartaric 

 acid, butalanine or amido-valerianic acid ; and of bases, ammonia, lysine, and 

 lysatinine. Besides these substances of known composition, there is another 

 substance of unknown composition formed, to which the name of tryptophan 

 has been given, although it has never been isolated, and is only known through 

 certain peculiar colour reactions which it gives. 



The amido-acids formed in tryptic digestion. 2 Leucine, Leucine 

 is an amidocaproic acid ((CH ? ) 2 CH.CH 2 .CH(:N T H 2 ).COOH), and is always formed 

 in any profound decomposition of proteid, such as boiling with dilute acids or 

 alkalies, fusing with alkalies, in tryptic digestion, or in putrefaction. It has 

 been found in nearly all the tissues in the body, and there has been much 

 discussion as to whether it is a normal constituent here, or is formed as a 

 post-mortem product. Certainly it is rapidly increased in amount, because of 

 proteid decomposition, after death, but the evidence is strong for its normal 

 presence in more or less pronounced traces in most of the organs in the fresh 

 condition. It is, besides, a very common constituent of tissue in many 

 pathological conditions, and also occurs in the vegetable world. 



Yirchow showed that both leucine and tyrosine are found normally in the 

 pancreas after death, and Kiihne afterwards showed that its amount here was 

 much increased by auto-digestion of the gland tissue post-mortem. 



Leucine was first discovered by Proust in 1818 in putrefying cheese, and 

 named by him cheese oxide (Kase-oxyd). It was also obtained by Braconnet 

 by decomposing animal matter with sulphuric acid. 3 



Leucine may be prepared in many ways : by tryptic digestion of proteid s, 

 by boiling various forms of proteid with dilute acids or alkalies, with stannous 

 chloride and hydrochloric acid, with bromine water in sealed tubes, or by 

 fusing with caustic alkalies. A common method is that of boiling horn 

 shavings with dilute sulphuric acid for many hours ; but any form of proteid 

 will yield it when so treated, such as meat, cheese, fibrin, wool, feathers, 

 elastic tissue. 



Leucine has been obtained artificially by Limpricht, 4 by acting on isoval- 



1 Skandin. Arch. f. Physiol., Leipzig, 1896, Bd. v. S. 277. 



2 For a very full account of these bodies, see Gamgee, " Physiological Chemistry of the 

 Animal Body," vol. ii. p. 231. 



3 Maly, Hermann's "Handbuch," Bd. v. (2), S. 207. 



4 Ann. de chim., Paris, 1854, tome xciv. p. 243. 



