THE END-PRODUCTS OF ALBUMINOUS DIGESTION. 203 



Several leucins apparently exist. One form, which can be pro- 

 duced synthetically from hydrocyanic acid and ammoniurn-iso- 

 valerianic aldehyde, is optically inactive. The common leucin, 

 on the other hand, which is formed during tryptic digestion or on 

 decomposition of the native albumins with hydrochloric acid, is 

 dextrorotatory. A third form results from the action of Penicilium 

 glaucum upon the inactive substance, and is said to be laBvorotatory. 

 An isoleucin has been obtained as a by-product in the production 

 of sugar from beets, and also is a component of various vegetable 

 and animal proteins. It corresponds to an a-amino-methyl-ethyl- 

 propionic acid : 



>CH.CHNH,.COOH. 



The common form is easily soluble in water, in alkalies and acids, 

 as also in hot alcohol ; in ether it is insoluble. It combines with 

 acids, alkalies, and the oxides of some of the heavy metals to form 

 salts. On boiling a solution of leucin with subacetate of lead the 

 corresponding compound of lead oxide can be obtained if ammonia 

 is carefully added to the cooled solution. A copper salt is similarly 

 formed if leucin in aqueous solution and containing a small amount 

 of alkali is treated with a solution of cupric sulphate, care being 

 taken not to add an excess. On standing, the compound separates 

 out in the form of clusters of blue needles, which are characterized 

 by their pronounced insolubility. 



When carefully heated to a temperature of 170 C. leucin melts 

 and sublimes in the form of white flakes, which are deposited on the 

 cooler portion of the tube. At the same time the odor of amylamin 

 develops. 



On evaporating a small amount of leucin upon platinum foil with 

 nitric acid a colorless residue is formed. If to this a drop of sodium 

 hydrate solution is added and heat is carefully applied, a yellowish 

 or brownish color develops, and on further heating an oil-like droplet 

 is obtained, which rolls about upon the platinum without adhering 

 (Scherer's test). 



On decomposition with an alkali or during the process of putre- 

 faction leucin yields ammonia and valerianic acid. On oxidation 

 leucinic acid results. 



As has been indicated, leucin is an amino-capronic acid of the 

 formula (CH 3 ) 2 .CH.CH 2 .CH(NH 2 ).COOH, and may hence be re- 

 garded as a-amino-isobutyl-acetic acid. 



Tyrosin. Tyrosin can be obtained on tryptic digestion from all 

 those albumins in which aromatic groups exist. Collagen, in which 

 this is absent, accordingly yields no tyrosin, and very small amounts 

 only are obtained from elastin. In the animal body it is practically 

 found as such only under pathological conditions if we disregard the 

 minute quantity which is found in the intestinal canal. Like leucin, 

 it is also formed during the process of albuminous putrefaction, and 



