PRODUCTS OF PANCREATIC DIGESTION. 



the body is an advanced decomposition product. The sub- 

 stance is sometimes called proteinochromogen. 



Ex. To recognize the chromogen or tryptophane use two or three cc. 

 of the above filtrate from the digestion experiment. Add to the liquid 

 some bromine water, drop by drop, shaking after each addition. Finally 

 the desired color appears. 



Tyrosine and Leucine. These important amino acids have 

 already been referred to when the decomposition products of 

 proteins were described. They are formed abundantly in a 

 prolonged digestion like the above and may be easily recog- 

 nized. Tyrosine is paraoxyphenyl-a-aminopropionic acid, 



/OH 

 C 8 H, < 



\CH 2 CH(NH 2 )COOH 



and is formed from most of the protein bodies on digestion. 

 It is not formed in appreciable quantity from gelatin. Leu- 

 cine is regarded as a caproic acid derivative, or possibly 

 as a-aminoisobutylacetic acid (CH 3 ) 2 CH.CH2.CH(NH 2 )- 

 COOH. It is one of the most common of the protein cleavage 

 products, and is formed from gelatin also. Both of these sub- 

 stances are but slightly soluble in cold water and may be eas- 

 ily separated in crystalline form. 



Ex. To recognize the two amino acids in the digestion mixture pro- 

 ceed as follows: Concentrate the bulk of the liquid to a volume of 25 cc. 

 and allow it to stand in a cold place several days. At the end of this time 

 filter through fine muslin or a coarse filter paper. The granular mass 

 so collected contains some tyrosine while the bulk of the leucine remains 

 in the filtrate. Examine the residue first. Wash it into a beaker with 

 a little cold water, allow to settle, decant and wash again by decantation. 

 Then add a larger volume of water and enough ammonia to give a marked 

 odor. Heat to boiling and filter hot. The tyrosine dissolves in the alka- 

 line liquid. Concentrate the filtrate until the odor of ammonia has dis- 

 appeared and allow to cool; crystals of tyrosine separate. 



Examine some of these under the microscope. The appearance is that 

 of bunches or sheaves of fine needles. These needles may be dissolved in 

 alkalies and also in hydrochloric acid on the slide, which behavior distin- 

 guishes them from other somewhat similar crystalline deposits. 



MILLOX'S TEST. A very distinctive test is by the use of Millon's reagent, 

 which has been already illustrated. Mix a little of the crystalline deposit 

 with some water and Millon's reagent in a test-tube and apply heat. A 

 13 



