24 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



of H2O2. In each case keep the volume of the mixture constant (with 

 distilled water). Determine if the speed of the catalase reaction increases 

 in direct proportion to the amount of enzyme; use several measured dilu- 

 tions of potato juice from the same sample. Vary also the concentration 

 of H2O2. 



Compare times required to produce the same amount of change. 



Repeat experiments immersing reaction-chamber (1) in ice water, (2) 

 in water at 30°, (3) at room temperature. The flask should be immersed as 

 far as possible in the water. 



If possible, analyse the thermal effect. The kinetics of these catalase 

 reactions are discussed by Northrop (J. Gen. Physiol., 7: 373, 

 1925; cf. also Williams, J. Gen. Physiol., 11: 309, 1928). 



DIGESTION OF STARCH BY PANCREATIC AMYLASE 



8. Effect of Concentration of the Substrate. — Measure into six clean 

 test tubes the following proportions of soluble starch solution and dis- 

 tilled water; mix thoroughly. 



Tube No 



H2O, cc 



Starch solution, cc 



Now add 0.5 cc. of the pancreatic amylase solution to each test tube, mix- 

 ing thoroughly and noting the time when the addition is made. Test 

 for the rate of digestion by the iodine method. This consists in removing 

 5 drops from each mixture and adding a drop of the dilute iodine solution. 

 During the course of digestion the color changes from blue through purple 

 to red. This red stage is known as the erythrodextrin point. A stable 

 solution of erythrodextrin is provided as a standard for colorimetric 

 matching, thus sharpening the end point. Note the time interval from 

 the beginning of the reaction to the erythrodextrin stage for each tube. 



Plot the results (cf. Haldane, "Enzymes," p. 31, 1930). (Preparation 

 of solutions. Add M to 3^ gram of pancreatin to 40 cc. H2O. Shake 

 thoroughly for at least five minutes. Filter through best quantitative 

 filter paper. This may take 3 hours. Obtain a clear filtrate. Add 

 filtrate to 500 cc. H2O. Test sample with starch solution to obtain a 

 reasonable digestion time. To prepare starch solution add 2 grams of 

 soluble starch to 500 cc. H2O. Boil 1 liter H2O and add solution little by 

 little. The solution must be clear and free from opalescence. Adjust 

 solution so that equal parts of enzyme solution and starch solution digest 

 in about 10 mins. at room temperature. Prepare standard erythrodextrin 

 solution and fix by heating at right stage. Do not add iodine until time 

 for comparison.) 



