807 
Our results show that the enzyme is not yet injured at nada, 
but is gradually injured at py = 4.095. However, in view of the 
relatively short duration (20 min.) of the digestion-experiments de- 
scribed above, the injury is, even in the case of py = 4.095 
only of small account. We conclude, therefore, that the inhibitory 
influence of the H-ions in concentrations beyond the optimal is not 
attributable to injury to the enzyme. 
In addition we have also tried to ascertain, whether the enzymic 
activity is weakened in fluids made slightly alkaline. 
ce 10 cc. of phosphoric acid, 27 c.c. of sodium hydrate, 13 cc. 
of water. Addition: 25 c.c. of enzyme R-+ 15¢.c. of water, all the 
amylum solutions as in the preceding test, py of the enzyme- 
mixture 8.718. 
Nr. prs commie) eg Reduction Rotation | 
was maintained const. at 37° | 
1 | 0 142.20 ee ries 
2 | 29.5 | 147.35 — | 6.02 
3 “55.5 rend a AE 
4 | 103.5 LAS se En 
5 | 255.0 140.70 = en 
6 380.5 134.55 =~ — 
Consequently no injury in two hours’ time with a faintly alkaline 
reaction, pa — 8.718. 
It is obvious, therefore, that in our experiments injury to the 
enzyme cannot have had any influence worth mentioning; on this 
account we could not expect the optimal reaction to shift in a 
prolonged digestion-test. Researches, each lasting 100 minutes, 5 times 
longer than the other ‘experiments, confirmed our supposition. 
Further experimentation will have to reveal the relation between 
the electric charge of ptyalin to its action, for which the iso-electric 
point has to be determined *). 
Summary. 
For the action of ptyalin the concentration of the hydrogen-ions is 
highly important. In fluids in which the reaction has been deter- 
1) Cf. MicHAELIS Bioch. Zeitschr, Bd. 35, S. 386, Bd. 36. S. 280, 
53% 
