CATALYSIS AND ENZYMES 317 



regard to emulsin (1912, 2), in which rabbits were injected with the enzyme, 

 led me to examine carefully the evidence as to the existence of anti-enzymes] 

 In the experiments referred to, it was found that a " precipitin " was formed 

 for the vegetable protein present as impurity in the emulsin used, but that 

 there was no precipitin for the enzyme itself. The serum, in point of fact, did 

 retard the action of emulsin, but the effect was found to be merely due to 

 diminution of the acidity of the solution ; when this was brought back to its 

 initial value by the addition of acid phosphate, the inhibitory effect disappeared. 

 Moreover, making an emulsin solution of the same hydrogen ion concentration 

 as that produced by the addition of "immune-serum" caused the same degree 

 of retardation. 



It is to be noted that " anti-emulsin " was the first anti-enzyme supposed to be produced 

 (Hildebrandt) ; it is generally regarded as a typical one and certainly has more evidence in its 

 favour than any other one. This evidence is discussed in my paper referred to above. When 

 the serum of an animal shows, normally, " anti-enzymic " properties, it is naturally impossible to 

 obtain satisfactory evidence that these can be increased by the injection of the enzyme in 

 question, since the property exhibits large natural variations. In other cases, adsorption 

 of enzymes by colloidal substances is sufficient to account for the " an ti " properties ; Hedin 

 (1906) showed that the adsorption of trypsin by charcoal is precisely similar to a typical 

 retardation by anti-enzymes. 



Thaysen (1915) finds that the so-called " anti-rennin " of serum is to be entirely 

 accounted for by the two influences referred to above, the adsorption of the 

 enzyme on the one hand, and the effect of change in hydrogen ion concentration, 

 as found by myself in the case of emulsin. There is no true antibody formed. 



We shall see later that enzymes are not proteins, at least the fact has been 

 definitely established in some cases and in none is there evidence of their being so. 

 This, in itself, is a priori reason for doubting the production of true antibodies, 

 until it has been shown that substances other than proteins can give rise to their 

 formation. 



Under special circumstances, substances preventing the action of enzymes 

 are to be met with. An interesting one is that present in intestinal ivorms, 

 protecting them from the action of trypsin. The properties of this substance 

 were especially investigated by Hamill (1906) and it was found to be soluble in 

 85 per cent, alcohol, not destroyed by boiling in neutral or acid solution, but 

 readily in alkaline solution. It is not a colloid. When added to a tryptic digest, 

 it is found to disappear slowly, so that ultimately the enzyme recovers its full 

 activity and is, therefore, merely temporarily paralysed. Its disappearance in the 

 alkaline digest is natural, owing to its sensibility to alkali. As will be seen, this 

 substance has none of the characteristics of Ehrlich's antibodies. 



The behaviour of raw serum or egg-white to trypsin is peculiar. If the curves 

 on p. 129 of my monograph (1913, 2) be referred to, it will be noticed that the 

 action on raw egg-white starts slowly but becomes more rapid until it ultimately 

 reaches the same point as when the substrate had been previously boiled. This may be 

 due to the presence of some inhibitory substance similar to that of the intestinal 

 parasites, or perhaps to the adsorption of the enzyme by the protein, which is 

 itself a difficult one for attack ; as this protein is slowly attacked, the enzyme is set 

 at liberty, so that it is available for the further conversion of the easily attacked 

 proteoses resulting from the initial hydrolysis of the protein. 



Concentration of Substrate. According to the law of mass action, it is to be 

 expected that the rate of change in an enzyme reaction would be directly 

 proportional to the concentration of the substrate. This is so, in the main, so long 

 as the concentration does not exceed a certain value, which differs in individual 

 cases. In that of caseinogen, for instance, below 5 per cent, the rate is 

 proportional to the concentration, although not in simple linear ratio ; above 

 5 per cent., the rate continues about the same up to 8 per cent., but in 10 per cent, 

 solution it is rather less than in one of 8 per cent. There appear to be two factors 

 concerned. The rate of a reaction in such colloidal heterogeneous systems, as we 

 have seen, is determined by the amount of the adsorption compound between 

 enzyme and substrate in existence at any given time. Remembering further what 

 we have learned with regard to adsorption in general, we see that, at a certain 



