82 PHYSIOLOGICAL CHEMISTRY. 



EXPERIMENTS. 



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 subsequent isola- 

 tion 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 in a 

 large flask with water containing 3-5 per cent of H 2 SO 4 and place 

 it on a water-bath until the protein material 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 

 proteases, 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 mo- 

 ments, filter it through a filter paper which has not been previously 

 moistened. After dissolving the precipitate of proteoses and pep- 

 tones in water 3 the solution may be treated according to the method 

 of separation given on page 114. 



The leucine and tyrosine, 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. 23, 

 page 72), followed later by the formation of characteristic crystals 

 of impure leucine (see Fig. 105, Chapter XX). After examining 

 these crystals under the microscope, strain off the crystalline material 

 through fine muslin, heat it gently in a little water to dissolve the leu- 



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. 



3 If the solution is alkaline in reaction at this point, the amino acids will be 

 broken down and ammonia will be evolved. 



8 At this point the aqueous solution of the proteoses and peptones may be 

 filtered to remove any BaSCV 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 al- 

 cohol filtrate. 



