22 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



isotherm (cf. Scarth and Lloyd, p. 160). For a general discussion of 

 colloids, cf. Thomas "Colloid Chemistry," 1934. Text p. 84. 



V. ENZYME ACTION 



Peroxidase and "Oxidase."— Prepare potato juice by scraping the 

 surface of potato with glass (not metal). Mix with an equal volume of 

 water, stir, strain through cheese cloth. Divide into equal portions. 

 Boil one for 5 minutes. In the tests use boiled solution as control in each 

 case. To separate portions: 



1. Add H2O2 and a few drops of gum guaiac solution (freshly prepared 

 alcoholic solution) on a slide. Text p. 400. 



2. Add guaiac solution alone. Compare with pulp from heart of 

 potato. Cf. Bayliss, p. 584. 



Catalase. — (Catalase is discussed by Meldrum, ' 'Cellular Respiration," 

 Chapt. IV, 1934. Stern has shown that catalase can attack organic 

 peroxides (monoethyl hydrogen peroxide to acetaldehyde). Text p. 400. 



3. To 5 cc. neutralized H2O2 in a test tube add 3 cc. crushed liver 

 suspension. Result? 



4. Repeat using liver previously boiled. 



5. Repeat with 



(a) 5 cc. fresh liver suspension plus 5 drops 10% HCl 



(b) with 5 cc. liver suspension plus 1 cc. 1% NaCOa solution 



(c) with liver suspension plus equal volume N/10 KCN 



(d) with liver suspension plus equal volume saturated HgCl2 solution 



6. Dehydrogenase. — Slightly color with methylene blue two tubes 

 of fresh unpasturized milk. Add a few drops of formaldehyde to one tube 

 and observe any decolorization of the dye which occurs (cf . Wieland's book 

 on "Oxidation," p. 57). 



Try the same test with yeast suspension. Allow to stand. The yeast 

 has H donors so addition of formaldehyde is unnecessary. 



7. The Kinetics of the Decomposition of H2O2 by Catalase. — (The cat- 

 alase extract can be prepared from potato or from liver. In the latter case 

 the assistant should determine a dilution which will evolve oxygen at a 

 rate suitable for measurement.) 



Place a constant volume of catalase extract (i.e., 10 cc.) in an Erlen- 

 meyer flask. By means of thread lower a small phial of H2O2 (upright) 

 into the flask. Connect the flask with a burette arranged to collect 

 the gas given off (the burette is filled with water and inverted over a finger 

 bowl of water). Start by tipping over the phial. With constant shaking, 

 record as frequently as possible the amount of gas given off. Determine 

 if the speed of the catalase reaction increases in direct proportion to the 

 amount of enzyme. Use several measured dilutions of catalase extract 

 FROM THE SAME ORIGINAL SAMPLE. Varv also the concentration 



