SPECIFICITY 



123 



of hydrochloric acid. Pepsin can hydrolyse about 400,000 times 

 its weight of caseinogen. 



{b) Do not Initiate Reactions. This is a much more difficult canon 

 to satisfy. Certainly cane sugar in solution slowly undergoes 

 inversion, but who is to say whether it would inv^ert in the process 

 of time if kept dry. The process might be proceeding at an 

 immeasurable rate. 



(c) Final State of Equilibriiun. Enzymes do appear to change 

 the equilibrium point of reversible reactions in some cases, e.g. 

 No Catalyst. Starch + HgO -^ dextrin + maltose -\- glucose 



Catalyst-HCl, ,, ,, — > glucose 



,, Amylase ,, „ -^ maltose. 



i.e. the reaction takes place in steps. In the presence of water all 

 the stages are shown, while when acid is added only the final 

 product appears in quantity. Various enzymes activate the 

 various steps — one enzyme aids in the production of dextrins 

 from soluble starch, another assists in the process of hydrolysing 

 the dextrins to maltose, while still another catalyses the step down 

 from maltose to glucose. Each of those steps should be considered 

 a separate reaction. 



- {d) Activation Proportional to Concentration. This is strictly 

 true of enzymes, and may be proved in various ways (Part II.). 



{e) Not Destroyed. That enzymes are altered during a reaction is 

 not surprising considering their unstable colloidal nature. The 

 change entailed is usually an alteration in physical state whereby 

 they are rendered inactive. 



(/) Specificity . Each enzyme acts on a specific substrate, and 

 if the substrate is a mixture of optical isomers, one of these (and 

 always the same one) will be selected for preferential treatment. 

 Examples may make this clearer. If maltase be added under 

 suitable conditions to the following disaccharides it will be found to 

 act preferentially on one — maltose. 



TABLE XX 



