ENZYMES 205 



tion produced by acids, etc., which act upon enzymes already ac- 

 tive, or with that produced by coenzymes. A coenzyme may be 

 separated from its enzyme and the action is reversible, which is 

 not the case with an activator and its zymogen. Trypsinogen, 

 secreted by the pancreas, has little action on proteins until it is 

 activated either by calcium salts or by the enterokinase secreted 

 by the intestine. 



Proenzymes have likewise been reported from plant tissues. 

 They are said to be present in the cells as small granules which dis- 

 appear when the zymogen has been activated. Thus prolipase 

 has been reported from castor beans, prooxidase from tobacco 

 leaves, and propapain from Carica (activated by HCN). The fact 

 that dilute acids and calcium salts are excellent activators of 

 zymogens has led Waldschmidt-Leitz to deny the existence of such 

 proenzymes. His position (and a not unreasonable one) is that 

 these zymogens are simply inactive because of improper pH or 

 some similar factor. The " activators" do nothing to the enzyme, 

 but merely change its environment to a more favorable one. 



Antienzymes. — An antienzyme is a substance occurring in the 

 living organism (or produced in it by the injection of an enzyme) 

 which prevents the action of an enzyme upon the tissue. Thus 

 intestinal worms and other parasites of the digestive tract must 

 secrete some antipepsin and antitrypsin as well as other anti- 

 enzymes to prevent their digestion by the digestive juices in their 

 environment. Similar enzymes probably exist in the lining of the 

 alimentary canal itself to prevent autodigestion. Since mosquito 

 larva can hatch and develop in the pitchers of pitcher plants, the 

 larvse probably contain antiproteases. In plants, antioxidases have 

 been reported by Czapek (1905), and it is reasonable to expect that 

 the protoplast must always contain antienzymes to protect itself 

 against the injurious action of the enzymes it secretes. Whether 

 these antienzymes are a specific group of compounds, however, is 



doubtful. 



Summary; Artificial Enzymes.— The reactions of plants at life 

 temperatures are hastened by organic catalyzers called enzymes. 

 These are probably proteinaceous in nature but owe their prop- 

 erties more to the fact that they are colloids than to the fact that 

 they are proteins. This is borne out by the experiments of Bredig, 

 who prepared colloidal catalysts from silver and other metals by 

 passing 110 volts of electricity between metal electrodes in a water 



