CH. XXVIII.] ACTION OF ENZYMES 443 



by writing the chemical equation connected by a double arrow 

 instead of the sign of equation. Two examples follow : 



C 2 H fi . OH + CH 3 . COOH ^_ C 2 H 5 . COO . CH 3 + H 2 O 



[Ethyl alcohol.] [Acetic acid.] [Ethyl acetate.] [Water.] 



C 6 H 12 6 + C C H 12 6 ^ C 12 H 22 O n + H 2 



[Dextrose.] [Laevulose.] [Cane sugar.] [Water.] 



This phenomenon is termed "reversibility," and was first demon- 

 strated by Croft Hill in his experiments with cane sugar and 

 invertase. 



In intracellular action this is a factor of importance, for the 

 same enzyme can in the presence of different proportions of the 

 substrate and its cleavage products both tie (in anabolism) and 

 untie (in katabolism) the knot. 



It should further be noted that hydrolytic actions are isothermic ; 

 that is, the total energy of the products is equal to that of the 

 substance broken up. 



The simpler logarithmic law of enzyme action has been demon- 

 strated for the majority of enzymes (invertase, trypsin, erepsin, 

 lipase, etc.). The effect in a given time is directly proportional to 

 the quantity of enzyme present. But there is an exception to this 

 rule in the case of pepsin, as was first pointed out by Schutz in 1885. 

 He found that peptic activity is proportional to the square root of 

 the amount of pepsin present. Thus if a certain quantity of pepsin 

 produced an amount of digestive action which we will call a, in 

 order to produce a digestive action equal to 2a in the same time, it 

 would be necessary to employ four times the amount of pepsin ; and 

 in order to produce a digestive action equal to 3a, it would be 

 necessary to use nine times the amount of pepsin. This rule 

 (Schiitz's law) has been often confirmed, and a few years ago 

 Arrhenius explained it on mathematical lines into which we need not 

 enter here. 



Anti-enzymes. Many chemical substances, such as strong acids 

 and alkalis, alcohol, formaldehyde, iodine, potassium cyanide, and 

 salts of the heavy metals, hinder enzyme activity. But the term 

 anti-enzyme is generally limited to substances produced in the 

 metabolism of living organisms. Excess of these organic anti- 

 enzymes can be readily produced by injecting an enzyme into the 

 blood-stream of an animal. This stimulates the production of an 

 anti-enzyme, so that when the blood-serum is mixed with the original 

 enzyme, its power is inhibited. Anti-enzymes are specific, that is, 

 they inhibit the enzyme which was injected into the blood, and no 

 other. 



