78 BACTERIAL METABOLISM ENZYMES 



does not occur. By means of this theorem it has been possible to 

 foretell the structure of many complex substances and explain 

 hitherto obscure points in biology. 



2. The chemical change brought about by an enzyme in infinite 

 time is independent of the concentration of the enzyme, but for 

 shorter periods it is clearly and usually a definite function of the 

 concentration of the enzyme. This means that a small quantity 

 of enzyme will bring about as much change as a large one, provid- 

 ing unlimited time is given. In this regard, then, enzyme reac- 

 tions differ from ordinary reactions in that they do not follow the 

 law of mass action. This may be illustrated by the carrying of 

 brick to the top of a building by men. Give one man sufficient 

 time and he would be as able to transfer the whole pile to the top 

 as would a group of men, but in the latter case the time occupied 

 would be inversely proportional to the number of men working. 

 So it is with enzymes; the intensity is almost directly proportional 

 to the concentration of the enzymes. In certain instances where 

 this generalization has been found not to hold, attempts have 

 been made to apply the Schutz-Borissow Law that the intensity 

 of enzyme reaction is directly proportional to the square root of 

 the concentration. But even this generalization does not hold, for 

 there are a number of factors which tend to retard or accelerate 

 enzyme action. Chief among these which retard are (a) reversi- 

 bility, (6) combination of enzyme with products, (c) negative 

 autocatalysis, which with the previous factor leads to reversible 

 inactivation of the enzyme, (d) destruction or similar drastic changes 

 in the properties of the enzyme. Those which accelerate are as 

 follows : (a) combination of the whole of the enzyme with the sub- 

 strate when the latter is in relatively large excess, (6) positive 

 autocatalysis. 



3. Reactions which are catalyzed by enzymes are reversible. 

 It has been conclusively shown in the case, of many reactions and 

 is generalized for others that where a reaction is being catalyzed by 

 enzymes it is, unless the products so formed are removed from the 

 reaction medium, reversible. This is illustrated by the saponifica- 

 tion of ethyl-butyrate by means of lipase. 



C 3 H 7 COOC 2 H5 + H 2 O = C 3 H 7 COOH + C 2 H 5 OH 

 Ethyl-butyrate. Butyric acid. Ethyl alcohol. 



Starting with a definite quantity of ethyl-butyrate, after a time 

 we find in the reacting media ethyl-butyrate, butyric acid and 

 ethyl alcohol; commencing with butyric acid and ethyl alcohol, we 

 obtain the same products as in the first case. This implies that the 

 synthetic reactions which are going on in the cell are catalyzed by 

 the same enzymes as are the analytic reactions; hence reactions 

 that are catalyzed by enzymes are never complete unless the result- 

 ing products are removed as fast as formed. 



