114 SPECIFIC NATURE OF CATALYTIC ACTION 



equally as in parasitic infection, willjlepend upon the individual 

 variations in the blood as a suitable medium for such a reaction, 

 upon the presence or absence of an anti-body at the outset capable 

 of neutralising the trace of auto-catalyst bearing the infection, and 

 upon the reactive power of the tissue cells to the auto-catalyst or 

 toxin. 



THE SPECIFIC NATURE OP CATALYTIC ACTION 



It has already been mentioned that enzymes are very specific 

 in their action, and in the character of the products which they 

 produce from the substratum. 



It has been well pointed out by Bredig that this cannot be 

 converted into a criterion for distinguishing the action of an 

 enzyme from that of an inorganic catalyst. For although such 

 specific action is seen at its maximum in the enzymes, it is also 

 observable in the action of many inorganic catalysts. Thus 

 while certain catalysts, such as the hydrogen ion, are very general 

 in their action, catalysing most hydrolytic reactions, such as cleav- 

 age of all disaccharides, amyloses, and esters, other catalysts are 

 quite elective in action. Examples quoted by Bredig are potassium 

 bichromate, which energetically catalyses the oxidation of hydriodic 

 acid by bromic acid, but does not act upon that of the same acid 

 by iodic acid or potassium persulphate ; iron and copper salts, 

 which intensely catalyse the oxidation of potassium iodide by 

 potassium persulphate, but not the oxidation of sulphurous acid 

 by the same oxidising agent. 



On the other hand, as also pointed out by Bredig, emulsin 

 in addition to hydrolysing the glucoside amygdalin with which 

 it is naturally associated, similarly acts upon many other sub- 

 stances, such as Arbutin, Helicin, Salicin, Phloridzin, Daphnin, 

 Coniferin, Aesculin, and Lactose. 



There is no doubt, however, although no fundamental difference 

 can be deduced therefrom, that the vast majority of the enzymes 

 are more highly selective in their action than the inorganic enzymes. 



Thus, as has been beautifully shown by the researches of 

 E. Fischer, an enzyme may act upon one stereo-isomer and not 

 upon the other, the action being thrown out by the change in 

 position of a single group. 



To use Fischer's striking analogy, the ferment and its sub- 



