70 ENZYMES 



terious effect upon most enzymes, and retard their rate of action ; 

 but, apparently, autolytic enzymes (Neuberg l ) and tyrosinase 

 (Willcock 2 ) are not injured by these agencies. Labile as enzymes 

 are, their persistence when dry is remarkable ; Kobert found 

 active trypsin in the bodies of spiders that had been in the 

 Nuremberg Museum for 150 years, andSehrt 3 found that the 

 muscle tissue of mummies contained active glycolytic ferment. 



All enzymes as ordinarily prepared have the property of 

 decomposing hydrogen peroxide, a property possessed by sub- 

 stances of varied nature; this effect is prevented by CNH, 

 which does not prevent other enzyme manifestations, indicating 

 that this property is due to an associated enzyme, catalase. 



The retardation of enzyme action by accumulation of the 

 products of their action is simply explained as being due to 

 establishment of equilibrium; in some instances, however, the 

 substances produced are of themselves harmful to the enzymes, 

 e. </., alcohol and acetic acid. 



Activation of Enzymes. Within the cell, the enzymes at 

 least those that are excreted, such as trypsin and pepsin exist 

 with few exceptions in an inactive form, the zymogen. Their 

 activation appears to take place normally only after they have 

 been discharged from the cell, but after the death of an organ 

 it may result from the decomposition products that are formed. 

 Under physiological conditions this activation appears to be 

 brought about by special activating substances. In the case of the 

 pancreas it is the enterokinase, which is furnished by the epithe- 

 lial cells of the intestine. Enterokinase appears to unite with 

 trypsinogen to form an active enzyme, which reminds one of the 

 way that complement and the intermediary body unite to form 

 hemolytic and bacteriolytic substances. 4 Kinases, having the 

 same action as enterokinase upon the trypsinogen, are found in 

 various tissues and organs, but generally much less active than 

 the enterokinase. Pepsinogen is probably activated by the HC1 

 of the gastric juice. A similar activating process seems to be 

 essential for the production of the glycolytic ferment of the 

 muscle and liver, the pancreas furnishing the activator in this 

 <case. It is very probable that it is through this mechanism 



' * Berl. klin. Woch., 1904 (41), 1081. 



2 Jour, of Physiol., 1906 (34), 207. 



3 Berl. klin. Woch., 1904 (41), 497. 



* Bayliss and Starling (Jour, of Physiol., 1905 (32), 129), question the anal- 

 ogy of zymogen-kinase combinations to complement-amboceptor combination. 

 Walker, however, finds evidence that many enzymes consist of a specific ambo- 

 ceptor and a non-specific complement or kinase (Jour, of Physiol., 1906 (33), 

 p. xxi.). 



