138 THE PROTEIN SUBSTANCES. 



3. The Amino Acids. 1 



Glycocoll (amino-acetic acid), C2H 5 NO 2 = AU 2 > also called glycine 



or gelatin sugar, is found in the muscles of the invertebrates, but has 

 chief interest as a hydrolytic decomposition product of protein bodies, 

 especially fibroin, spider-silk elastin, gelatin, and spongin, as well as of 

 hippuric acid and glycocholic acid. It is also formed in the decomposi- 

 tion of uric acid, xanthine, guanine, and adenine. 



Glycocoll forms colorless, often large, hard rhombic crystals or four- 

 sided prisms. The crystals have a sweet taste and dissolve readily in 

 cold water (4.3 parts). Glycocoll is insoluble in alcohol and ether and dis- 

 solves with difficulty in warm alcohol. It combines with acids and alkalies. 

 With the latter compounds we must mention those with copper and 

 silver. Glycocoll dissolves cupric hydroxide in alkaline liquids, but does 

 not reduce at boiling heat. A boiling-hot solution of glycocoll dissolves 

 freshly precipitated cupric hydroxide, forming a blue solution, which in 

 proper concentration deposits blue needles of copper-glycocoll on cool- 

 ing. The compound with hydrochloric acid is readily soluble in water 

 but less soluble in alcohol. 



SoRENSEN 2 finds that phosphotungstic acid does not precipitate 

 glycocoll from dilute solutions but only from concentrated ones. By the 

 action of gaseous HC1 upon glycocoll in absolute alcohol, beautiful 

 crystals are obtained of the hydrochloride of glycocoll ethyl ester, which 

 melts at 144 C. and from which the glycocoll ethyl ester can be obtained 

 by the method suggested by E. FISCHER 3 for the separation of glycocoll 

 from the other amino-acids. On shaking with benzoyl chloride and 

 caustic soda, hippuric acid is formed, and this is also made use of in 

 different ways in detecting and isolating glycocoll (Cn. FISCHER, GON- 

 NERMANN, SpiRO 4 ). The /?-naphthalene-sulpho-glycine with a melting- 

 point of 159, the 4 nitro-tolulene-2-sulpho-glycine, melting at 180, 

 the phenylisocyanate compound, melting at 195, and the a-naphthyl- 

 isocyanate compound melting at 190.5-191.5 are also of importance. 



Glycocoll can be best prepared from hippuric acid by boiling it with 

 4 parts dilute sulphuric acid (1:6) for ten to twelve hours. After cooling 

 the benzoic acid is removed, the filtrate concentrated, the remaining 

 benzoic acid removed by extracting with ether, the sulphuric acid pre- 



1 In regard to the division of the animo-acids among the three chief groups of 

 organic compounds we refer to page 85. 



2 Meddelelser, fraa Carlsberg-laboratoriet, 6, 1905. 



3 Ber. d. d. chem. Gesellsch., 34. 



4 Ch. Fischer, Zeitschr. f. physiol. Chem., 19; Spiro, ibid., 28; Gonnermann, 

 Pfliiger's Arch., 59. 



