AMIDO-ACIDS FORMED IN TR YPTIC DIGESTION, 425 



during which time most of both the leucine and tyrosine crystallises out. After 

 separation of the crystals, the filtrate may be once more reduced in bulk by 

 evaporation and a second crop of crystals obtained as before. 



To the syrupy mother-liquor now remaining absolute alcohol is added, until 

 precipitation of the peptone commences, when the addition of alcohol is 

 stopped and the precipitate of peptone redissolved by gently warming. The 

 solution is now set aside to cool and crystallise as before. The united crops of 

 crystals of mixed leucine and tyrosine are boiled with alcohol, which dissolves 

 the leucine and but little of the tyrosine. On concentrating this alcoholic extract, 

 leucine crystallises out and may be purified by recrystallisation from alcohol. 

 From the residue insoluble in alcohol the tyrosine is obtained by dissolving in 

 weak ammonia water and neutralising. 



The yield, both of leucine and tyrosine, obtained from different materials 

 varies greatly, but in all cases the former is always formed in much larger 

 quantity. The following table l gives the percentage yield of the substances 

 obtained in some cases ; the figures indicate parts per 100 : 



Aspartic acid, or amido-succinic acid [C 2 H 3 .(NH 2 ).(COOH) 2 ], does not 

 occur in any of the animal tissues or secretions, but is formed in small 

 quantity in all those decompositions of proteids and their allies already described 

 as furnishing leucine and tyrosine. 2 It was first identified among the products 

 of pancreatic digestion of fibrin by Radziejewski and Salkowski, 3 and von 

 Knieriem afterwards showed that it is also formed in the pancreatic digestion 

 of plant glutin. 



It may also be obtained by decomposing asparagin (amido-succinamic acid) 

 by an alkali or acid, thus : 



CH 2 COOH 



CH(NH 2 ) CO(NH 2 ) + HC1 + H 2 

 (asparagin or amido-succinamic acid). 



CH 2 COOH 



CH(NH 2 ) COOH 



(aspartic acid or amido-succinic acid). 



* Compiled from Maly, Hermann's "Handbucli," Bd. v. (2), S. 209 et seg. 



2 Ritthausen and Kreuster, Journ. /. prakt. Chem., Leipzig, 1871, Bd. iii. S. 314 ; 

 Hlasiwetz and Habermann, Ann. d. Chem., Leipzig, 1871, Bd. clix. S. 304. 



3 Radziejewski and E. Salkowski, Ber. d. deutsch. chern. Gesellsch., Berlin, 1874, Bd. vii. 

 S. 1050 ; Ann. d. Chem., Leipzig, 1873, Bd. clxix. S. 150 ; W. v. Knieriem, Ztsehr. f. BioL, 

 Miinchen, 1875, Bd. xi. S. 198. From 100 pts. of dry egg albumin Hlasiwetz aud 

 Habermann obtained 23 '8 pts. of aspartic acid by the action of bromine in sealed tubes, 



