216 Dr. G. Senter. [June 2, 



for example, may form with the enzyme compounds which are inactive 

 towards hydrogen peroxide. If the affinity between haemase and the 

 acid is small, in other words, if the enzyme acts as a weak base, the 

 amount combined, and consequently the retardation will be propor- 

 tional to the strength of the acid. We have already seen that 

 haemase and most other enzymes are rendered inactive by small 

 quantities of alkali, and that they regain their activity on the solution 

 being neutralised. These facts seem to lend some support to a 

 suggestion I have already made on a former occasion,* that at least 

 some enzymes belong to the class of amphoteric substances which are, 

 under ordinary circumstances, neutral, but in the presence of bases 

 develop acid properties and can combine with acids to form salts. 

 Within the last few years it has been shown that many albuminous 

 substances are amphoteric. 



The slight retardation caused by most neutral alkali salts is due,- in 

 all probability, to increased viscosity of the solution. This cannot 

 apply, however, to the considerable toxic effect of the chlorine and 

 bromine ions and, since a similar retardation of the platinum catalysis 

 has been observed, it may be due to some action between the hydrogen 

 peroxide and halogen salts. Kastle and Loevenhartf regard the 

 retardation of the platinum catalysis as due to the formation of surface 

 films of the insoluble platinous halides. 



The retarding influence exerted on the action by oxidising agents 

 is very remarkable. It is not due to oxidation of the enzyme in most 

 cases, as is clear from the fact that the constants do not decrease during 

 the action in presence of potassium perchlorate and nitric acid. On the 

 other hand, potassium chlorate in exceedingly dilute solution seems to 

 oxidise the enzyme, and since the neutral salt itself has very weak 

 oxidising properties, its activity in this case must be due to the presence 

 of the peroxide. That it is due to chloric acid set free by the hydrogen 

 peroxide, acting as an acid, is scarcely likely, since the acidic properties 

 of the latter are very weak. In this connection it is interesting to 

 note that potassium persulphate has very little effect on the action, 

 whereas persulphuric acid has a high oxidation potential. 



The great retardation caused by some reducing agents, such as 

 sulphuretted hydrogen and hydroxylamine, is also rather difficult to 

 account for. Bredig} suggests that the poisonous effect of the former 

 on the platinum catalysis is due to the deposition of sulphur on the 

 surface of the platinum, whereas Kastle and Loevenhart regard it as 

 being due to formation of a surface film of platinum sulphide. Neither 

 of these explanations seems to apply to the effect on the hsemase catalysis, 

 since I have observed that the constants increase considerably during 



* Loc. cit., p. 301. 



f Loc. tit. 



I Loc. oil., p. 87. 



