46 CHEMISTRY OF THE PROTEIDS CHAP. 



A high percentage is usually in the raceme form. The melting- 

 point is 203-204 . 1 It tastes very sweet. 2 



E. Fischer raised at once the question whether pyrrolidin-carboxylic 

 acid is a primary dissociation-product, or whether the pyrrol-ring is 

 liberated through the agency of the strong hydrochloric acid from 

 another less dissociated disintegration product, such as an amino- 

 valerianic acid, glutaminic acid, or an oxy-acid. The formation of the 

 a-pyrrolidin-carboxylic acid by the transformation of an open chain 

 into a ring-like structure he had observed himself under the action of 

 hydrochloric acid. 3 On dissociating casein by means of 10 per cent 

 soda solution, he obtained approximately the same amount of pyrrolidin- 

 carboxylic acid as after the dissociation with hydrochloric acid, 4 but 

 as during the esterification strong hydrochloric acid had to act on the 

 dissociation-products, he does not as yet consider the question definitely 

 settled. 



The attempt to solve the question by tryptic digestion is not pos- 

 sible, as trypsin does not liberate the pyrrolidin-carboxylic acid at all 5 

 But although the question is as yet an open one, E. Fischer 6 points 

 out that the percentage -amounts of pyrrol -derivatives and of the 

 diamino-acids agree. 'The .quantitative relation between the cyclic 

 acid and the diamino-compounds seems to be a general one, and makes 

 it probable that both have an origin in common.' 7 On boiling, how- 

 ever, diamino-acids with hydrochloric acid no pyrrolidin-carboxylic 

 acid is formed, 5 according to Kossel and Dakin. 8 



23. Hydroxy-a-pyrrolidin-carboxylic Acid, or Hydroxy- 

 prolin, C 5 H 9 N0 3 . 



This acid also was discovered by E. Fischer 9 amongst the dissocia- 

 tion-products of gelatine, but the position of the oxy-group is not yet 

 settled. It crystallises from the residue after the esters of the amino- 

 acids have been distilled off, and after the diamino-acids have been 

 precipitated by means of phosphotungstic acid. It has also been found 

 in casein, 7 globin, and edestin, and may be even more widely dis- 

 tributed. As to the possibility of this acid being formed secondarily, the 

 same arguments hold good as were advanced for the previous acid. It 

 is leevo-rotatory : 



1 E. Fischer, P. A. Levene, and E. H. Aders, Ber. d. deutsch. chem. Ges. 35. 70 

 (1902). 



2 E. Fischer, ibid. 35. HI. 2660 (1902). 3 E. Fischer, ibid. 34. I. 454 (1901). 



4 E. Fischer, Zeitschr. f.physiol, Chem. 35. 227 (1902).' 



5 E. Fischer and E. Abderhalden, ibid. 39. 81 (1903) 



6 E. Fischer and E. Abderhalden, ibid. 36. 268 (1902). 



7 E. Fischer, ibid. 39. 155 (1903). 



8 Kossel, Berliner klinische Wochensch. No. 41, Oct. 1904, p. 1065. 



9 E. Fischer, Ber. d. deutsch. cfom. Ges. 35. III. 2660 (1902). 



