32 CHEMISTRY OF THE PROTEIDS CHAP. 



one of the albumins he examined the substances alanin, phenylalanin, 

 a-pyrrolidin-carboxylic acid, glutaminic and aspartic acids. As re- 

 gards quantity, however, in most albumins leucin exceeds by far the 

 other dissociation-products. 1 The older figures of Cohn, 2 Proscher, 3 

 and Erlenmeyer and Schoffer, 4 who found about 40 per cent of leucin 

 in casein, globin, and elastin, are certainly too high, for they based 

 their figures on the ' Roh fraction,' of which leucin only forms a part. 

 From such an impure product E. Fischer 5 obtained by means of the 

 ester method only about one-third of pure leucin, and he goes fully 

 into the difficulties he experienced in separating, by means of re- 

 crystallisation, 6 leucin from other closely-related amino-acids, such as 

 amino-valerianic acid. Most of the leucin obtained from albumin is 

 said to be contaminated with a substance containing nitrogen and 

 sulphur. 7 But even pure leucin, the preparation of which is accompanied 

 by great loss, makes out a very large portion of the dissociation-pro- 

 ducts. Abderhalden found in globin 8 30 per cent, in serum albumin 9 

 20 per cent, in edestin 10 20 '9 per cent, all these figures representing 

 minimal values, as explained above when describing the ester method. 



As was pointed out above, leucin is a-amino-isobutyl-acetic 

 acid, 11 and therefore contains a branched carbon chain. This fact 

 distinguishes it sharply from lysin, the diamino-normal-caproic acid 



According to E. Fischer, 12 leucin obtained from albumins is Meucin, I 

 as in watery solutions it is laevo-rotatory ; in acid or alkaline solutions 

 it is, however, dextro-rotatory. According to E. Schulze and Winter- 

 stein, 13 in hydrochloric acid of 24 per cent strength 



a D = +18-9. 



Leucin is soluble in 46 parts of water. 14 



E. Fischer 12 has examined d, I, and ?'-leucin, as well as a series of 



1 For an exception see under glutaminic acid, p. 35. 



2 R. Cohn, Zeitschr.f.physiol. Chem. 22^153 (1896), 26. 395 (1899). 



3 F. Proscher, ibid. 27. 114 (1899). 



4 Erlenmeyer and A. Schoffer, Journ. f. prakt. Chem. (1) 80. 357 (1860). 



5 E. Fischer, Ber. d. deutsch. diem. Ges. 34. I. 433 [p. 446] (1901). 



6 E. Fischer, ibid. 34. I. 433 [p. 446] (1901) ; and ibid. 33. II. 2370 

 (1900). 



7 E. Fischer, ibid. 33. II. 2370 (1900). 



^ 8 E. Abderhalden, Zeitschr. f. physiol. Chem. 37. 484 (1903). 

 Vg E. Abderhalden, ibid. 37. 495 (1903). 

 ^ E. Abderhalden, ibid. 37- 499 (1903). 



11 E. Schulze and Likiernik, ibid. 17. 513 (1893) ; B. Gmelin, ibid. 18. 21 

 (1893). 



12 E. Fischer, Ber. d. deutsch. chem. Ges. 33. II. 2370 (1900). 



13 E. Schulze and E. Winterstein, Zeitschr. f. physiol. Chem. 35. 299 (1902). 



14 B. Gmelin, ibid. 18. 21 (1893). 



