186 CHEMISTRY OF PLANT LIFE 



may vary widely in chemical composition; and that their tre- 

 mendous catalytic effects are due, in part at least, to their colloidal 

 nature. This will be better understood and appreciated after the 

 phenomena associated with the colloidal condition have been 

 considered (see the following chapter). 



NOMENCLATURE AND CLASSIFICATION 



Since nothing is known of the chemical composition of enzymes, 

 they can only be studied by considering the effects which they 

 produce. This is reflected in the systems which have been adopted 

 for their nomenclature and classification. 



As they were first supposed to be proteins, the earlier repre- 

 sentatives of the group were given characteristic names ending 

 with the suffix in, similar to that of the proteins. Since this idea 

 has been found to be incorrect, however, a system of nomen- 

 clature has been adopted which assigns to each enzyme the name 

 of the material upon which it acts, followed by the suffix ase. 

 Thus, cellulase is the enzyme which accelerates the hydyrolysis 

 of cellulose; glucase, that acting upon glucose; amylase, that 

 acting upon starch (amylum), etc. 



The substance upon which the enzyme acts (or, strictly speak- 

 ing, the substance whose hydrolysis, oxidation, or other chemical 

 change, is catalytically affected by the enzyme) is called the 

 substrate. 



Most enzymes are catalysts for hydrolysis reactions and are, 

 hence, classed as hydrolytic in their action, and may be spoken 

 of as " hydrolases." Those which accelerate oxidation are 

 called " oxidases"; while those that stimulate reduction reactions 

 are " reductases"; those that aid in the splitting off of ammonia, 

 or amino-acid groups, are " deaminases"; and those that aid in 

 the splitting off of CCb from COOH groups are " carboxylases," 

 etc. 



The hydrolytic enzymes are further sub-divided into the 

 sucroclastic (sugar-splitting), or sucrases; the lipoclastic (fat- 

 splitting), or lipases; the esterases (ester-splitting); proteoclastic 

 (protein-splitting), or proteases; etc. 



