V] CARBOHYDRATES 77 



demonstrated [see Expt. 57 (a) and (b)] in connexion with dextrin. The 

 following experiments have special reference to the enzyme. 



jEJxpt. 78. To demonstrate the activity of diastase from germinating barley. {See 

 also Expt. 57.) 



Pound up 2-3 gins, of germinated barley grains in a mortar and extract the mass 

 with 50 c.c. of water. Filter, and take two equal portions in two test-tubes. Boil one 

 tube. To both tubes add an equal quantity of the starch solution prepared as in 

 Expt. 55. Place the tubes in a beaker of water at 38-40° C. From time to time 

 withdraw a drop from each tube with a pipette and test with iodine solution on a 

 white tile. The starch in the unboiled tube will gradually give the dextrin reactions 

 (see p. 59) ; that in the boiled tube will remain unchanged. 



This simple method may also be adopted for showing the diastatic activity of 

 leaves. Instead of germinating barley, a few leaflets of the Pea {Pisum sativum) or 

 Clover {Trifolium pratense) should be pounded up in a mortar and extracted with 

 50 c.c. of water and filtered. 



Maltase. This enzyme hydrolyzes maltose into two molecules of 

 glucose: 



C12H22O11 + H2O = 2C6H12O6. 



Investigations upon maltase have, until recently, produced rather 

 contradictory results, but later work (Davis, 14: Daish, 15, 16) has led 

 to more satisfactory conclusions. The latter show that maltase is most 

 probably present in all plants in which hydrolysis of starch occurs. It 

 has been detected in leaves of the Nasturtium {Tropaeolum), the Potato 

 {Solarium), the Dahlia, the Turnip (Brassica), the Sunflower (Helianthus) 

 and the Mangold (Beta), and it is most probably widely distributed in 

 foliage leaves. Its detection is not easy for various reasons which are 

 as follows. It is not readily extracted from the tissues by water : it is 

 unstable, being easily destroyed by alcohol and chloroform. Its activity 

 is also limited or even destroyed at temperatures above 50° C. Hence 

 the extraction of maltase, by merely pounding up tissues with water, 

 does not yield good results : moreover, as an antiseptic, toluol must be 

 used and not chloroform. Finally, if the enzyme is to be extracted from 

 dried material, this must not be heated at too high a temperature previous 

 to the extraction. 



Maltase occurs in quantity in both germinated and ungerminated 

 seeds of cereals. If, in kilning, malt has not been heated at too high a 

 temperature, the maltase may not be destroyed, and, in such cases, malt 

 extract will contain both diastase and maltase. This would explain the 

 fact that glucose, instead of maltose, has sometimes been obtained by 

 the action of malt diastase on starch. In other cases, when a higher 

 temperature has been employed, the maltase will be destroyed. Maltase 



