14 PHYSIOLOGICAL CHEMISTRY 



An experiment similar to Experiment 4, page 197, may also be tried if desired. 

 In this experiment 0.2 c.c. of either ethyl butyrate or amyl acetate may be employed. 



IV. INVERTASES 1 



1. Preparation of Vegetable Sucrase. 2 Thoroughly grind about 100 grams of 

 brewer's or baker's yeast in a mortar with sand. Spread the ground yeast in thin 

 layers on glass or porous plates and dry it rapidly in a current of dry, warm air. 

 Powder this dry yeast, extract it with distilled water and filter. Pour the filtrate 

 into acetone, stir and after permitting the acetone mixture to stand for a few min- 

 utes filter on a Buchner funnel. The resulting precipitate, after drying and 

 pulverizing, may be used to demonstrate vegetable sucrase. 



2. Demonstration of Vegetable Sucrase. To about 5 c.c. of a i per cent 

 solution of sucrose in a test-tube add a small amount of the sucrase powder pre- 

 pared as directed above. Place the tube at 38C. for 24-72 hours and at the end 

 of that period test the solution by Fehling's test (see page 25.) Reduction indi- 

 cates that the active sucrase powder has transformed the non-reducing sucrose 

 into glucose and fructose, and these sugars, in turn, have reduced the Fehling 

 solution. 



For other experiments on Invertases, see Chapter XI. 



V. OXIDASES 3 



i. Demonstration of Oxidase. Oxidases or oxidizing enzymes con- 

 stitute a very important group of intracellular enzymes. They are 

 intimately connected with the oxidation processes in the plant and ani- 

 mal organisms. 



1. Cut a thin slice from a freshly pared potato, place it on a watch glass and 

 examine at intervals during the laboratory exercise. Note that the colorless 

 potato gradually becomes brown. 



This is due to the oxidation of para-oxyphenyl substances such as 

 tyrosine, in the cells and in the intracellular juice of the potato. Two 

 oxidases which have the power of accelerating the oxidation of para- 

 oxyphenyl compounds are called tyrosinase and laccase. 



2. Preparation of Potato Extract. Scrape a pared potato by means of a knife 

 or scalpel or comminute the potato substance by means of a grater. Extract the 

 macerated potato substance by means of water. Strain through cheese cloth and 

 filter the extract. Make an iodine test on the solid substance (see Starch, page 

 45), and save the water extract for use in the following experiments. 



3. Oxidation of Para-oxyphenyl Compounds by Potato Oxidases. Introduce 

 5 c.c. of filtered potato extract prepared as indicated above, into each of six test- 

 tubes. Introduce additional reagents into the tubes according to the following 

 series: 



(a) Potato extract -f 5 drops of toluene (control). 



(b) Potato extract + 5 drops of ether (control). 



1 The inverting enzymes of the alimentary tract; Mendel and Mitchell: American Journal 

 of Physiology, 20, 81, 1907-08. 



* For a discussion of this enzyme see p. 198. 



8 These experiments have been adapted from directions contained in the Laboratory 

 Notes of Professor Gies of the College of Physicians and Surgeons, New York. 



