400 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



A series of drops of iodine solution are placed upon a porcelain 

 plate, or upon a glass plate on white paper. 5 c.c. of starch solution 

 are placed in each of two test tubes, 5 c.c. of diastase solution 

 is placed in the one and 5 c.c. of boiled diastase solution in the other. 



The second tube acts as a control. The hydrolysis proceeds more 

 rapidly at 40 so that the test tubes are placed in a bath at this tem- 

 perature. 



A drop is removed from each solution immediately after the mix- 

 tures have been made and placed against an iodine drop. 



The mixture in the first tube soon becomes less opaque, if starch 

 paste solution has been used. 



At intervals of half a minute, or a minute, drops are removed from 

 each test tube and placed against another iodine drop. The blue colour 

 given by the control tube is given each time the test is made, but the 

 colour becomes reddish-brown in the case of the other tube and finally 

 no colour at all is given. Achroodextrin and maltose have been 

 formed. Each test tube, after about 5 minutes, is tested with Feh- 

 ling's solution. The control tube shows no reduction, but the pres- 

 ence of maltose in the other tube is shown by a marked reduction. 



Effect of Temperature, o, 45, 1 00, upon Diastase. 



The same experiment is performed with two test tubes con- 

 taining 5 ac. of starch solution and 5 c.c. of diastase solution, but 

 one of them is placed in cold water, or better, ice, and the second 

 in a water- bath at 45. The time when the various colours are given 

 and when no colour is given with the iodine drops is noted 



The hydrolysis takes place more slowly in the tube kept at the 

 lower temperature. A third test tube is prepared containing 5 c.c. 

 of starch solution, but to it is added 5 c.c. of boiled and cooled diastase 

 solution. It is placed in the bath at 45. A drop taken from this 

 tube will give a blue colour with iodine. The enzyme has been 

 destroyed by boiling. 



In experiments with enzymes a control experiment is carried out 

 with boiled enzyme solution instead of water. The enzyme solution 

 usually contains other substances besides the enzyme and the same 

 amount of these is added to the substrate in each experiment. It is 

 extremely important to carry out such a control experiment, especi- 

 ally in cases where a rough measurement has to be made to demonstrate 

 enzyme action, e.g. in the cases of lactase and maltase. 



Effect of Acid, Alkali and Salt upon Diastase. 



5 c.c. of starch solution, I c.c. of water and 5 c.c. of saliva solution 

 are placed in one test tube. 



5 c.c. of starch solution, I c.c. of dilute hydrochloric acid (*iN or 

 0-4 per cent) and 5 c.c. of saliva solution are placed in a second test 

 tube. 



