ENZYMES AND THEIR ACTION II 



of a minute remove a drop of the solution to one of the depressions of a test-tablet 

 and test by the iodine test. 1 If the blue color with iodine still forms after five 

 minutes, add another 5 drops of saliva. 



The opalescence of the starch solution should soon disappear, 

 indicating the formation of soluble starch (amidulin) which gives a blue 

 color with iodine. This body should soon be transformed into erythro- 

 dextrin which gives a red color with iodine, and this, in turn, should 

 pass into achroodextrin which gives no color with iodine. This point is 

 called the achromic point. When this point is reached test by Fehling's 

 test 2 to show the production of a reducing substance (maltose). A 

 positive Fehling's test may be obtained while the solution still reacts red 

 with iodine, inasmuch as some sugar is formed from the soluble starch 

 coincidently with the formation of the erythrodextrin. For further 



discussion of the transformation of starch see page 55. 



> 



2. Demonstration of Pancreatic Amylase. 3 Proceed exactly as indicated above 

 in the Demonstration of Salivary Amylase except that the saliva is replaced by 5 c.c. 

 of pancreatic extract prepared as described on p. 192.* Pancreatic amylase trans- 

 forms the starch in a manner entirely analogous to the transformation resulting 

 from the action of salivary amylase. 



3. Preparation of Vegetable Amylase. Extract finely ground malt with water, 

 filter and subject the filtrate to alcoholic fermentation by means of yeast. When 

 fermentation is complete filter off the yeast and precipitate the amylase from the 

 filtrate by the addition of alcohol. The precipitate may be filtered off and ob- 

 tained hi the form of a fine white powder. 



A purer preparation 5 is obtained if the solution is dialyzed against 

 water at about ioC. (in the ice-box) for 24 hours, filtered and pre- 

 cipitated with alcohol or acetone. First alcohol or acetone to make a 50 

 per cent solution is added, the precipitate thus formed being rejected, 

 while the precipitate formed on the addition of sufficient alcohol or 

 acetone to make a final concentration of 65-70 per cent is preserved, and 

 dried in a vacuum desiccator at a low temperature. 



4. Demonstration of Vegetable Amylase. This enzyme may be demon- 

 strated according to the directions given under Demonstration of Salivary Amylase, 

 page 10, with the exception that the saliva used in that experiment is replaced by 

 an aqueous solution of the vegetable amylase powder prepared as described 

 above. 6 



1 See p. 43- 



2 See p. 25. 



8 For a discussion of this enzyme see p. 190. 



4 Commercial preparations of pancreatic amylase may be substituted for the pancreatic 

 extract. 



6 Sherman and Schlesinger: /. Am. Ch. Soc., 35, 1617, 1915. 



6 If desired the first aqueous extract of the original malt may be used in this demonstra- 

 tion. Commercial taka-diastase may also be employed 



