PROTEINS 85 



lose their water of crystallization they assume a characteristic violet 

 color. 



Oxyproline, C 5 H 9 NO3. Oxyproline was discovered by Fischer. 

 It has as yet been obtained from only a few proteins, but this may be 

 due to the fact that only a few have been examined for its presence. 

 The position of the hydroxyl group has not yet been established. 



Diaminotrihydroxydodecanoic Acid, Ci2H 2 6N 2 05. This ammo acid 

 was discovered by Fischer and Abderhalden as a product of the hydro- 

 lysis of casein. It has thus far been obtained from no other source. 

 It is levo-rotatory and its constitution has not been determined. 



EXPERIMENTS 



Protein Decomposition. While the ordinary courses in physiological 

 chemistry preclude any extended study of the decomposition products 

 of proteins, the manipulation of a simple decomposition and the sub- 

 sequent isolation and study of a few of the products most easily and 

 quickly obtained will not be without interest. 1 To this end the student 

 may use the following decomposition procedure. 



Treat the protein (coagulated egg albumin) in a large flask with water con- 

 taining 3-5 per cent of H 2 SO 4 and place it on a water-bath until the protein ma- 

 terial has been decomposed and there remains a fine, fluffy, insoluble residue. 

 Filter off this residue and neutralize the filtrate with Ba(OH) 2 and BaCO 3 . 

 Filter off the precipitate of BaSO 4 which forms and when certain that the fluid is 

 neutral or faintly acid, 2 concentrate (first on a wire gauze and later on a water- 

 bath) to a syrup. This syrup contains the end-products of the decomposition of 

 the protein, among which are proteoses, peptones, tyrosine, leucine, etc. Add 

 95 per cent alcohol slowly to the warm syrup until no more precipitate forms, 

 stirring continuously with a glass rod. This precipitate consists of proteoses and 

 peptones. Gather the sticky precipitate on the rod or the sides of the dish and, 

 after warming the solution gently for a few moments, filter it through a filter 

 paper which has not been previously moistened. After dissolving the precipi- 

 tate of proteoses and peptones in water 3 the solution may be treated according to 

 the method of separation given on page 120. 



The leucine and tyrbsine, etc., are in solution in the warm alcoholic filtrate. 

 Concentrate this filtrate on the water-bath to a thin syrup, transfer it to a beaker, 

 and allow it to stand over night in a cool place for crystallization. The tyrosine 

 first crystallizes (Fig. 25, page 76), followed later by the formation of characteristic 



1 The procedure here set forth has nothing in common with the procedure by means 

 of which the long line of decomposition products just enumerated are obtained. This 

 latter process is an exceedingly complicated one which is entirely outside the province of 

 any course in physiological chemistry. 



2 If the solution is alkaline in reaction at this point, the amino acids will be broken^ 

 down and ammonia will be evolved. 



3 At this point the aqueous solution of the proteoses and peptones may be filtered to 

 remove any BaSO 4 which may still remain. Tyrosine crystals will also be found here, 

 since it is less soluble than the leucine and may adhere to the proteose-peptone precipitate. 

 Add the crystals of tyrosine to the warm alcohol filtrate. 



