54 CHEMISTRY OF THE PROTEIDS CHAP. 



tryptophane would then not be an a-amino-acid. 1 Only a synthesis 

 can, however, clear up this matter. See also under Kynurenic Acid, 

 p. 84. 



Tryptophane, as prepared by the method of Hopkins and Cole, has 

 very strong reducing powers, as the chlorides of gold, platinum, and 

 palladium are reduced in a few seconds, the metals passing through 

 a soluble colloidal state into an insoluble form (Mann). 2 



Tryptophane has been prepared by Hopkins and Cole up till now 

 in a pure state from casein, fibrin, egg-white, and serum albumin ; 

 but, judging by the tryptophane reaction and indol formation, it must 

 exist in most albumins. If one divide albumins into a hemi- and into 

 an anti-group (see p. 148) then, according to Pick 3 and E. Fischer 

 and Abderhalden, 4 tryptophane belongs, along with tyrosin, to the 

 hemi-group. It is, therefore, absent from gelatine 5 and from 

 hetero-albumose. 3 



In the older works of Nencki, Beitler, and Kurajeff mention is 

 made of several colouring matters, but it is difficult to say whether 

 one is dealing simply with impurities, or whether tryptophane may be 

 bromated to different degrees, or whether, in addition to tryptophane, 

 still other chromogens are present in albumins. The bromo-trypto- 

 phane is insoluble in water, chloroform, benzene, ether, and petroleum 

 ether, very slightly soluble in alcohol, but readily soluble in acetic ester 

 and amyl-alcohol. A solution in amyl-alcohol gives an absorption band 

 between 571 and 540 ///z. Through the discoveries of Hopkins and 

 Cole, and Ellinger, the older statements as to the existence of an indol 

 nucleus in tryptophane have been confirmed, and Nencki's assumption 

 of a relationship between tryptophane and the melanins is verified, for 

 Hopkins and Cole have observed that tryptophane is very liable to 

 change into brown-coloured substances on being boiled with acids or 

 merely with water. For this reason tryptophane is usually absent 

 amongst the dissociation -products, which are obtained by treating 

 albumins with acids. 



The derivatives of tryptophane are carriers of still another colour 

 reaction the so-called pyrrol reaction. If one immerse a chip of 

 pinewood, e.g. a wooden match, into strong hydrochloric acid, and 

 then place it in a watery solution of indol, it will gradually become of 



1 Levene has described amino-acids which are not o-amino-acids (Levene, Zeitschr. 

 f.physiol. Chem. 41. 100 (1904). 



2 Gustav Mann, Physiological Histology, 1902, p. 269. 



3 E. P. Pick, Zeitschr. f. physiol. Chem. 28. 219 (1899). 



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



5 R. Maly, Monatsh. /. Chem. 10. 26 (1889) ; M. Nencki, Ber. d. deutsch. chem. 

 Ges. 7. II. 1593 (1874). 



