34 CHEMISTRY OF THE PROTEIDS CHAP. 



Serin was discovered by Cramer 1 amongst the dissociation-products 

 of silk, and hence its name. E. Fischer 2 first demonstrated its wide 

 occurrence and also determined its composition. 3 Up till now it has 

 not been missed in any albumin, although generally it is only present 

 in small quantities, a circumstance which is partly due to the great 

 difficulty of its preparation. 4 Serin occurs also in gelatine to the extent 

 of, at least, 0*4 per cent. 5 While iso-serin is /3-amino-a-oxypropionic 

 acid, serin is a-amino-/3-oxypropionic acid, and is therefore closely 

 related to cystein, which is thio-serin. 6 A ready means of synthetising 

 serin has been found by Erlenmeyer, 7 and Fischer and Leuchs. 8 

 Ellinger has also converted diamino-propionic acid into iso-serin. 9 



In watery solutions it does not rotate. 3 It tastes sweet. 10 E. 

 Fischer 2 emphasises how important it is to find also in serin, i.e. 

 amongst the simple amino-acids, an oxy-amino acid. He suspects some 

 relationship to the carbohydrates, inasmuch as he regards glucosamin 

 as a link between the hexoses and the oxy-amino acids. 11 



6. Amino-tetrahydroxy-caproic Acid, C 6 H 13 N0 6 



OH OH OH OH NH 2 .0 

 H C C C C C C^ 

 H H H H H X OH. 



This acid has been isolated by Neuberg and Orgler from cartilage 12 

 (see later). They have also synthetised it. 



7. Aspartic Acid, C 4 H 7 N0 4 



Ov H NH 2 .0 



}C C C Of 

 H0 / H H X OH, 



is amino-succinic acid, or the Aminobernsteinsaure of the Germans. 

 It was first discovered and estimated quantitatively by von Ritthausen, 13 

 Avho dissociated vegetable albumins with sulphuric acid. By means of 



1 E. Cramer, Journ. f. prakt. Chem. [1] 96. 76 (1865). 



2 E. Fischer and A. Skita, Zeitschr. f. physiol. Chem. 35. 221 (1902). 



3 E. Fischer and H. Leuchs, Ber. d. deutsch. chem. Ges. 35. III. 3787 (1902). 



4 E. Fischer and T. Dorpinghaus, Zeitschr. f. physiol. Chem. 36. 462 (1902) ; E. 

 Fischer, ibid. 39. 155 (1903). 



5 E. Fischer and E. Abderhalden, ibid. 32, 540 (1904). 



6 E. Friedmann, Hofmeisters Beitr. 3. 1 (1902). 



7 E. Erlenmeyer, jun., Ber. d. deutsch. chem. Ges. 35. III. 3769 (1902). 



8 E. Fischer and H. Leuchs, ibid. p. 3790. 9 A. Ellinger, ibid. 37. 335 (1904). 



10 E. Fischer, ibid. 35. HI. 2660 (1902). 



11 E. Fischer and H. Leuchs, ibid. 36. I. 24 (1903). 



^ 12 Neuberg and Orgler, Zeitschr. f. physiol. Chem. 37. 407 (1904). 



13 H. Ritthausen, Journ. f. prakt. Chem. (1) 106. 445 (1869) ; H. Ritthausen and 

 U. Kreusler, ibid. (2) 3. 314 (1871). 



