152 THE PROTEIN SUBSTANCES. 



HOFMANN'S Test. If some water is poured on a small quantity of 

 tyrosine in a test-tube and a few drops of MILLON'S reagent added and 

 then the mixture boiled for some time, the liquid becomes a beautiful 

 red and then yields a red precipitate. Mercuric nitrate may first be 

 added, then, after this has boiled, nitric acid containing some nitrous 

 acid. 



DENIGES' Test, modified by G. M6RNER, 1 is performed as follows: 

 To a few cubic centimeters of a solution consisting of 1 vol. formaline, 

 45 vols. water, and 55 vols. concentrated sulphuric acid add a little 

 tyrosine in substance or in solution and heat to boiling. A beautiful 

 permanent green coloration is obtained. 



Proline (a-pyrolidine carboxylic acid), C 5 H9NO2 = H 2 C CH.COOH, 



NH 



was first obtained by E. FISCHER and then by FISCHER and collaborators 2 

 from several proteins. The proline here obtained was generally the 

 levo-rotatory modification. The largest quantity of proline was secured 

 from the vegetable protein hordein, namely, 13.7 per cent, and also from 

 the egg membrane of the Testudo graeca, 11.8 per cent (see table pages 

 106, 107, 114 and 124). KOSSEL and DAKIN 3 got 11 per cent from 

 salmine. Proline also occurs in scombrine and clupeine, but not in 

 sturine, which, according to KOSSEL, seems to contradict the view as 

 to the common origin of ornithine and proline. 



SoRENSEN, 4 by means of a general method of preparing a-amino-acids 

 synthetically, has prepared a -amino-<5-oxy valeric acid from phthalimide- 

 malonic ester and has obtained proline from this by evaporating with 

 hydrochloric acid, at the same time splitting off water. Recently he 

 has suggested another method which yields good results. Other syn- 

 theses of proline have also been performed by E. FISCHER and WILL- 



STADTER. 5 



Z-Proline crystallizes in flat needles. It is readily soluble in water 

 and alcohol. The solution has a sweet taste; the specific rotation at 

 20 C. is (a) D = 77.40. The solution acidified with sulphuric acid is 

 precipitated by phosphotungstic acid. In the detection of this acid we 

 make use of the copper salt, the anhydride of the phenylisocyanate 

 compound (melting-point 144), and the picrate (ALEXANDROFF 6 ). 



1 DenigSs, Compt. rend., 130; C. Th. Morner, Zeitschr. f. physiol. Chem., 37. 



2 E. Fischer, Zeitschr. f. physiol. Chem., 33 and 35. See also footnote 2, page 85. 



3 Zeitschr. f. physiol. Chem., 41. 



4 Zeitschr. f. physiol. Chem., 44; with A. C. Anderson, ibid., 56. 



5 Ber. d. d. chem., Gesellsch., 33. 

 8 Zeitschr. f . physiol. Chem., 46. 



