150 THE PROTEIN SUBSTANCES. 



Though taurine shows no positive reactions, it is chiefly identified 

 by its crystalline form, by its solubility in water and insolubility in alcohol, 

 by its combination with mercuric oxide, by its non-precipitability by 

 metallic salts, and above all by its sulphur content. 



CeH 5 



CH 2 . 

 Phenylalanine (phenyl-a-aminopropionic acid), C9H n NO2 = CH(NH 2 ), 



COOH 



was first found by E. SCHULZE and BARBIERI l in etiolated lupin sprouts. 

 It is produced in the acid cleavage of protein substances in quantities 

 given on pages 106, 107, 114 and 124. It has been prepared syntheti- 

 cally in several ways by ERLENMEYER JR., SORENSEN and E. FiscHER. 2 

 The /-phenylalanine crystallizes in small, shining leaves or fine needles 

 which are rather difficultly soluble in cold water but readily soluble hi 

 hot water. The solution has a faint bitter taste. A 5-per cent solution 

 acidified with hydrochloric acid or sulphuric acid is precipitated by 

 phosphotungstic acid, while a more dilute solution is not precipitated. 

 On putrefaction, phenylalanine yields phenylacetic acid. On heat- 

 ing with potassium dichromate and sulphuric acid (25-per cent) an odor 

 of phenylacetaldehyde is produced and benzoic acid is formed. In 

 aqueous solution it has a rotation of (a) D = 35.1. The phenyliso- 

 cyanate-phenylalanine melts at about 182 C. 



C 6 H 4 (OH) 



Tyrosine (p-oxyphenyl-a-aminopropionic acid), CgH n NO 3 = 



COOH 



is produced from most protein substances under the same conditions as 

 leucine, which it habitually accompanies. The largest quantity of tyro- 

 sine obtained from animal proteins was about 10 per cent (see tables, 

 pages 106, 107, 114 and 124). In gelatin and a few keratins tyrosine 

 is absent. It is especially found with leucine, in large quantities^ in old 

 cheese (Tv/oos), from which it derives its name. Tyrosine has not been 

 found with certainty in perfectly fresh organs. It occurs in the in- 

 testine in the digestion of protein substances, and it has about the same 

 physiological and pathological importance as leucine. 



Tyrosine was prepared by ERLENMEYER and LIPP from p-amino- 

 phenylalanine by the action of nitrous acid, and according to another 

 method by ERLENMEYER and HALSEY. S On fusing with caustic alkali 



1 Ber. d. d. chem. Gesellsch., 14, and Zeitschr. f. physiol. Chem., 12. 



2 Erlenmeyer, Annal. d. Chem. u. Pharm., 275; Sorensen, Zeitschr. f. physiol. 

 Chem., 44; E. Fischer, Ber. d. d. chem. Gesellsch., 37. 



3 Erlenmeyer and Lipp, Ber. d. d. chem. Gesellsch., 15; Erlenmeyer and Halsey, 

 ibid., 30. 



