ENZYMES 45 



amount of enzyme is sufficient to carry out the change 

 in large quantities of substance. 



Enzymes in great variety exist in the living body, 

 each kind acting upon a particular class of substance. 

 Thus the Upases l facilitate the hydrolysis of fats, 

 which are decomposed into simpler substances ; the 

 proteases have a similar action upon proteins. Of the 

 enzymes which work, upon carbohydrates, diastase, 

 which converts starch into sugar, is the best known. 

 The first stage of the reaction produces dextrin (a 

 soluble polysaccharide of the same empirical formula 

 as starch) and maltose : 



(C 6 H 10 5 ) n + H 2 0-->(C 6 H 10 5 ), + C 12 H 22 U 



starch water dextrin maltose 



The molecule of maltose is hydrolysed (its hydrolysis 

 being catalysed by another enzyme, maltase) into two 

 molecules of glucose : 



C 12 H 22 O n + H 2 = 2C 6 H 12 6 



maltose water glucose 



Invertase similarly catalyses the hydrolysis of sucrose 

 into one molecule of glucose and one molecule of the 

 closely allied sugar Icevulose : 



C 12 H, 2 O n + H 2 = C 6 H ]2 6 + C 6 H 12 6 



sucrose water glucose laevulose 



Cytases facilitate the hydrolysis of the celluloses into 

 simpler soluble carbohydrates. 



. Many, if not all, of the enzymes have what is called 

 a reversible action, i.e. they may bring about a change 

 in either direction, e.g. of starch into sugar, or of sugar 

 into starch. The direction in which the reaction actually 

 proceeds at any given moment depends upon the rela- 



1 The uniform termination -ase is used in the naming of enzymes. 



