ENZYMES AND ENZYMATIC ACTION 14 1 



Their action is inhibited at low temperatures and is destroyed 

 by boiling. Each enzyme also acts best in media of a certain 

 reaction as regards acidity or alkalinity. Some act in acid 

 media, some in alkaline, some in neutral. The concentration 

 of acidity or alkalinity is often quite definite and the action is 

 inhibited or even destroyed by a different concentration or by 

 a change from acid to alkaline or vice versa. It is impossible 

 to say whether the enzymes that have been isolated are pure 

 and individual substances or not. 



Reactions Brought About by Enzymes 



The reactions which enzymes bring about are of several kinds, 

 viz. hydrolysis, oxidation, reduction, coagulation and decomposi- 

 tion without extra-molecular oxidation, reduction or hydrolysis. 

 The reaction of hydrolysis takes place with either carbohy- 

 drates (di- and poly-saccharoses), fats or proteins. With the 

 carbohydrates hydrolysis results in the resolving of the poly- 

 saccharoses into their constituent monosaccharose units, e.g. 

 sucrose into glucose and fructose, starch into maltose and this 

 into glucose. With fats, which are glycerol esters, the hydrol- 

 ysis splits the molecule into its constituent glycerol and fatty 

 acid or acids. With proteins hydrolytic cleavage yields poly- 

 peptides and finally amino-acids. These reactions as such have 

 each been discussed under the study of the different com- 

 pounds concerned. In their final products the results of 

 enzymatic hydrolysis and of acid hydrolysis are the same. 



Hydrolyzing Enzymes. — The hydrolyzing or hydrolytic 

 enzymes are defined further according to the compounds upon 

 which they exert their catalytic effect, e.g. 



Starch-hydrolyzing enzymes are amylolytic, 



Sugar- hydrolyzing enzymes are sugar- splitting (saccharoly tic) , 



Protein-hydrolyzing enzymes are proteolytic, 



Fat-hydrolyzing enzymes are lipolytic, 



Glucoside-hydrolyzing enzymes are glue aside- splitting. 

 These hydrolytic enzymes are, as we shall find, mainly con- 

 cerned in the digestion and metabolism of plants and animals. 



