152 LECTURE VIII. 



Both proline and oxy-proline have been found in the decomposition 

 products of most albumins. The first is invariably present. It is, of 

 course, a question whether we are dealing with primary products. It is 

 possible that they are produced secondarily from another substance by 

 ring formation. Sorensen * has suggested that the primary substance in 

 the production of proline may be a-amino-d-hydroxyvaleric acid. We 

 have not yet succeeded in isolating the amino-hydroxy valeric acid, and 

 it must be remembered that a-proline is obtained by alkali hydrolysis, 

 as well as by acid. 2 A small amount of proline has also been obtained 

 by peptic 3 and tryptic 4 digestion. We have nothing at hand at present 

 to warrant us in excluding a-proline and oxy-proline as primary albumin 

 decomposition products. 



Tryptophane also belongs to this class of amino acids. It had been 

 known for a long time, that especially in tryptic digestion mixtures 5 some 

 substance was present which was characterized by certain color reactions. 



In an acetic acid solution it gives with chlorine or bromine water a violet 

 color. Also, if we insert a pine splinter, which has been previously dipped 

 into hydrochloric acid and then rinsed off, into a concentrated tryptophane 

 solution, the stick will turn purple on drying. This is the so-called pyrrole 

 reaction. It was soon shown that many of the reactions characteristic of 

 the albumins were due to the presence of tryptophane. If we add a little 

 glyoxylic acid, and then concentrated sulphuric acid, to a water solution 

 of albumin, a beautiful blue- violet coloration appears. 0. Neubauer and 

 Rohde 8 have indicated recently a new reaction for tryptophane in albumin. 

 If we add to a water solution, or suspension, of albumin, 5 to 10 drops of a 

 5 per cent solution of p-dimethyl-amino-benzaldehyde containing 10 per 

 cent of sulphuric acid, and then, while shaking, cautiously pour into the 

 solution a little concentrated sulphuric acid, a reddish-violet coloration 

 appears, which soon takes on a beautiful reddish violet shade. The 

 absorption spectrum shows a wide, faint band in tl^e orange (X 615-670), 

 and a second, obscure, band in the green (X 555-540) . 



F. G. Hopkins and Cole 7 were the first to prepare tryptophane in a pure 



1 S. P. L. Sorensen: Compt. rend. trav. Lab. Carlsberg, 6, 137 (1905); Z. physiol. 

 Chem. 44, 448 (1905). 



2 E. Fischer: Z. physiol. Chem. 36, 227 (1902). 



8 Commercial pepsin was used in these experiments. The possibility, therefore, 

 remains that other tissue ferments might have acted in conjunction with the pepsin, 

 for the reason that the commercial preparation is obtained by extracting the mucous 

 lining of the stomach. 



4 E. Fischer and E. Abderhalden: Z. physiol. Chem. 40> 215 (1903). 



Cf. E. Stadelmann: Z. Biol. 26, 491 (1890). R. Neumeister: ibid. 26, 324 (1890). 

 M. Nencki: Ber. 28, 560 (1895)- 



6 E. Rohde: Z. physiol. Chem. 44, 161 (1905). 



7 F. G. Hopkins and S. W. Cole: J. Physiol. 27, 418 (1901); 29, 451 (1903). 



