1904.] Studies on Enzyme Action. 215 



apparently no strongly oxidising intermediate peroxides are formed,* 

 nor is " active " oxygen evolved. It was also found that the action 

 has exactly the same initial velocity whether the solutions be carefully 

 freed from dissolved oxygen by a current of hydrogen, or whether, as 

 usual, a little of the former gas be present. 



The Action of Poisons. The question as to the mechanism of the 

 action of " poisons " on the hsemase catalysis of hydrogen peroxide may 

 now be considered. If the enzyme exists as a colloid in solution several 

 explanations! seem possible : 



(a) Part of the enzyme may be rendered inactive by forming a, 

 chemical compound with the poison. 



(b) Part of the surface of the particles may become covered with a 

 thin layer of the poison or one of its decomposition products, thus 

 preventing further action on the peroxide. 



(c) The relation of the particles to the surrounding medium may be 

 altered in various ways (change of surface tension, alteration of 

 relative difference of potential, &c.) through addition of a poison. 



Doubtless other explanations may be suggested. It is also exceed- 

 ingly probable that all poisons do not act in the same way. 



In this connection it may be noted that, according to Kastle and 

 venhart, the retarding effect of poisons on the catalysis of H^Og 

 y metals and other inorganic catalysors is due in most cases to 

 formation of an insoluble film (compound between poison and catalysor) 

 on the surface of the catalysor. 



The action of acids and alkalies on the hsemase catalysis is of parti- 



ar interest, since it has been shown, more especially by Hardy, | 

 ,t minute traces of these bodies affect profoundly the relation 



tween the colloidal particles and the surrounding medium. According 

 to Linder and Picton, Hardy, || and others, the effect of acids in 

 precipitating colloids is proportional to their electrical conductivity, 

 i.e., to the hydrogen ion concentration, but this is probably not 

 connected with the similar effect on the haemase catalysis because the 

 former action is irreversible, whereas I have shown that the latter is 

 reversible. It cannot be said that any very satisfactory explanation 

 of the effect of acids, alkalies, and other electrolytes on colloids has 

 yet been given. || 



With regard to the reaction under consideration I am inclined, in 

 most cases, to favour a chemical explanation of the toxic effect. Acids, 



* Or, if formed, their velocity of decomposition, either of themselves or in 

 contact with hydrogen peroxide, is much greater than the reaction velocity 

 between them and such a reducing substance as arsenious oxide. 



t Compare Bredig, loc. cit., p. 86. 



t 'Roy. Soc. Proc.,' vol. 66, p. 110 (18991900). 



Linder and Picton, ' Journ. Chem. Soc.,' vol. 67, p. 66 (1895). 



|| Vide Hardy, loc. cit., p. 124 ; Bredig, loc. cit., pp. 922 ; Freundlich, ' Zeit. 

 phys. Chemie,' vol. 44, p. 129 (1903). 



VOL, LXXIV. R 



