14 PHYSIOLOGICAL CHEMISTRY. 



two tubes at 38 C. for 2-3 days. At the end of that period heat 

 the contents of each tube to boiling, filter and try the biuret test 

 on each filtrate. In making these tests care should be taken to use 

 like amounts of filtrate, potassium hydroxide and cupric sulphate 

 in each test in order that the drawing of correct conclusions may be 

 facilitated. The contents of the tube which contained the boiled 

 extract should show a deep pink color with the biuret test, due to 

 the peptone still present. On the other hand the biuret test upon 

 the contents of the tube containing the unboiled extract should be 

 negative or exhibit, at the most, a faint pink or blue color, signify- 

 ing that the peptone, through the influence of the erepsin, has been 

 transformed, in great part at least, into amino acids which do not re- 

 spond to the biuret test. 1 



VI. URICOLYTIC ENZYME.' 



1. Preparation of Uricolytic Enzyme. Extract pulped liver 

 tissue with toluene- or chloroform-water at 38 C. for 24 hours, 

 with occasional shaking. Filter the extract and use the filtrate in 

 the following experiment. 



2. Demonstration of Uricolytic Enzyme. Add about o.i 

 gram of uric acid to 10 c.c. of water and bring the uric acid into 

 solution by the addition of the minimal quantity of potassium hy- 

 droxide. To 5 c.c. of this uric acid solution, in a test-tube, add 5 

 c.c. of the uricolytic enzyme extract prepared as described above. 

 Prepare a second tube containing a like amount of uric acid solution 

 but boil the extract before it is introduced. Place the two tubes 

 at 38 C. for 3-4 days and titrate the two digestive mixtures with 

 a solution of potassium permanganate according to directions given 

 under Folin-Shaffer Method, Chapter XXII. It will be found that 

 the mixture containing the boiled extract requires a much larger 

 volume of the permanganate to complete the titration than the other 

 tube. This indicates that a uricolytic enzyme has destroyed at least 

 a portion of the uric acid which was originally present in the tube 

 containing the unboiled extract. 



VII. CATALASE. 



Demonstration of Catalase. The various animal tissues, such 

 as liver, kidney, blood, lung, muscle and brain contain an enzyme 



1 Strictly speaking this erepsin demonstration is not adequate unless a control 

 test is made with native protein (except caseinogen, histones and protamines) 

 to show that the extract is trypsin-free and digests peptone but not native 

 protein. 



2 Mendel and Mitchell ; American Journal of Physiology, 1908, XX, p. 07. 



