76 BACTERIAL METABOLISM ENZYMES 



instead of "lytic," giving us terms such as "amyloclastic," "proteo- 

 clastic," "lipoclastic," etc. 



Enzymes ordinarily do not occur active within the cell, but 

 are present in the form of a zymogen or mother substance. This 

 substance, when acted upon by a specific substance, becomes 

 active and the process is termed "activation." The agency which 

 is instrumental in activating a zymogen is termed " zymo-excitor" 

 or kinase. 



Properties of Enzymes. Enzymes are known from the reactions 

 which they catalyze and they are found to follow quite definite 

 laws in their reactions. Some of the more important are as follows: 



1. An enzyme does not initiate a chemical reaction but only 

 alters its velocity; nor does it appear in the final products of the 

 reaction which it accelerates. We must, therefore, assume that 

 substances are slowly changing and that the catalyst does nothing 

 more than alter the speed of this reaction. The state of affairs is, 

 therefore, similar to that of a mixture of oxygen and hydrogen 

 gases catalyzed by platinum in which there is evidence that the 

 combination takes place at room temperatures, although at an 

 unmeasurable rate. Salicin, which is readily hydrolized by ptyalin 

 and emulsin to glucose and saligenin slowly decomposes in water 

 at 150 C. It would, therefore, be inferred that the process also 

 takes place at room temperature. Starch solutions slowly undergo 

 a spontaneous change into dextrin and sugar and solutions of 

 ammonium caseinogenate increase in electrical conductivity when 

 left to themselves, a change similar to that which occurs when 

 they are acted upon by trypsin. Taylor has shown that an appreci- 

 able proportion of pure sterile globulin kept in distilled water at 

 ordinary temperature for eighteen months is hydrolyzed to protease 

 and that leucin may be recovered from a sterile suspension of casein 

 in pure water and that arginin may be recovered from a solution 

 of protamin sulphate in pure water. True, the reaction is slow and 

 the products have accumulated only in small quantities after the 

 lapse of a year; nevertheless, it is evident that the process is slowly 

 occurring in the absence of the catalyzer. 



It is likely that the ferment enters temporarily into chemical 

 combination with the substance acted upon. This assumption is 

 made on the ground that the sensitiveness of the enzyme often 

 changes when brought in contact with the substrate and may at 

 first be hard to separate. Moreover, it i& definitely known that in 

 some simple catalytic processes the catalyzer does temporarily 

 combine with the reacting substance. This is the case in the 

 manufacture of sulphuric acid, where steam, sulphur dioxid, oxygen 

 and the oxids of nitrogen are introduced simultaneously into a 

 large chamber when the following reactions probably occur. 



SO 2 + N 2 O 3 = SO 3 + 2NO 

 SOa + H 2 O = H 2 SO 4 

 2NO + Oz = 2NO 2 



