50 BACTERIOLOGICAL CHEMISTRY 



nature of the groups in enzymes Avliich are responsible 

 for their activity. 



Some substances of known or unloiown constitution 

 may act as specific inhibitors of certain enzymes, and 

 such substances have been called anti -enzymes. Thus 

 normal serum contains an anti-trypsin which prevents its 

 activity ; this anti-trypsin is possibly a polypeptide 

 which combines with trjrpsin to the exclusion of its 

 normal substrate. The intestinal wall contains an anti- 

 pepsin by which pepsin is prevented from digesting the 

 tissue proteins. Heparin, a preparation obtained from 

 liver and used to prevent the clotting of blood, is an anti- 

 prothrombin which hinders the clotting of blood in the 

 veins by preventing the interaction of prothrombin and 

 calcium ions to form thrombin. Anti-enzymes in the 

 immunological sense are also known ; for instance, if the 

 enzyme amylase is injected into rabbits it produces an 

 anti-amylase Avhich specifically inhibits the action of the 

 enzyme. If malt-amlyase is injected the anti-enzyme 

 inhibits only malt amylase and not the salivary or pan- 

 creatic amylases. Similar antibodies specific for urease 

 and ribonuclease have also been prepared. An interesting 

 example is afforded by the a-toxin of Clostridium welchii 

 which has been shown to be essentially a lecithinase 

 whose action is specifically inhibited by CI. welchii 

 antitoxin. 



The Specificity of Enzymes. — Enzymes differ from the 

 majority of inorganic catalysts in being highly specific 

 in their action, and this is particularly true of the hydro - 

 lytic enzymes. Enzymes which hydrolyse proteins will 

 not have any effect on fats or on carbohydrates, nor will 

 carbohyrdate splitting enzymes hydrolyse proteins or 

 fats. The specificity goes even deeper than this ; maltase, 

 for instance, will hydrolyse only those sugars which 

 have the same type of linkage betAveen the glucose 

 molecules as occurs in maltose, that is, it will only attack 

 the a-glucose bond. Emulsin, on the other hand, will 



