1904.] Studies on Enzyme Action. 205 



exactly the same retardation, benzole, succinic, and acetic acids, which 

 are only partly dissociated, have considerably less effect in equivalent 

 concentration when, however, the concentration in hydrogen ions is 

 calculated (see second column), HC1, H 2 S0 4 , behzoic acid and succinic 

 acid have exactly the same retarding effect, that is, the retardation is 

 proportional to the hydrogen ion concentration. Nitric acid is more, 

 and acetic acid less, poisonous than would be expected from the 

 hydrogen ions present, and it is natural, in these two cases, to suggest 

 that the negative ions exert an influence. This has been shown to be 

 the case, as will be mentioned more fully later. While the Cl and S0 4 

 ions exert comparatively little influence, potassium nitrate slows down 

 the action to about the same extent as nitric acid itself. On the other 

 hand, sodium acetate has more accelerating influence on the reaction 

 than any other substance that has been tried. 



I may here mention that, although from considerations of space 

 only one series of results has been given, three series of measurements 

 have been carried out at different times with different enzyme prepara- 

 tions, and exactly corresponding results obtained, so that the figures 

 quoted may be accepted as reliable. 



Another interesting point about the behaviour of acids is that the 

 time during which the acid remains in contact with the enzyme before 

 the H 2 02 is added has no influence on the result ; the equilibrium is 

 attained within 5 minutes, and remains unaltered at the end of 2 or 

 3 hours. The change is not a permanent one, since if the acid, after 

 an incubation period of 2 hours, be neutralised before the addition of 

 the H 2 2 , the action proceeds with its original velocity. 



Kahlenberg* and his assistants have made a systematic investigation 

 of the toxic action of acids on small plants and on fishes, with the 

 object of finding whether the electrolytic dissociation theory is capable 

 of explaining the results. They find that the toxic effect is in the first 

 instance proportional to the hydrogen ion concentration, though there 

 are often secondary effects due to the other ions, and in all probability 

 to undissociated molecules. Similar results have been obtained with 

 seedlings by Cameron and Breazeale.f 



FernbachJ and others have made systematic investigations of the 

 effect of acids on enzyme actions. Fernbach gives a table containing 

 the amounts of different acids just sufficient to inhibit the action of 

 invertase on sugar, and from his numbers, and the dissociation constants 

 of the respective acids given by Ostwald, I have calculated the hydrogen 

 ion concentrations of the solutions in question ; the results are given 

 below : 



* Kahlenberg and Austin, 'Journ. phys. Chem.,' vol. 4, p. 553 (1900) ; Kahlen- 

 berg and Mehl, loc. cit., vol. 5, p. 113 (1901). 



t ' Journ. phys. Chem.,' vol. 8, p. 1 (1904). 



J These, Paris, 1890, quoted by Effront, ' Enzymes,' English Edit., 1902, p. 69, 

 et seq. 



