THE NATURE OF ENZYME ACTION 291 



occurrence of the reverse reaction was capable of accounting 

 for the greater part of the deviation from the unimolecular 

 logarithmic law, so that much more regular values were found 

 for the velocity constant when calculated from expressions 

 including terms taking this reverse reaction into account. It 

 did not seem, nevertheless, that the whole of the falling-off from 

 the logarithmic curve could be explained in this way. Visser 

 introduces the idea of " intensity " of action of the enzyme which 

 is in some way diminished as the reaction proceeds. In some 

 instances, in which the enzyme is one sensitive to changes of 

 chemical reaction, it seems possible that the influence of the 

 products of reaction may be partly accounted for in this manner. 

 Trypsin is very sensitive to alkali, and the various amino-acids 

 formed by its action may, by combining with alkali, diminish 

 the intensity of the tryptic action. This is a point requiring 

 investigation. 



The consideration just mentioned leads us back to the 

 peculiarity of the velocity of reaction of invertase. This is 

 found neither to proceed in accordance with the strict logarith- 

 mic law nor to fall away from it, but, on the contrary, to become 

 more rapid than the law requires. In other words, the activity 

 of the enzyme appears to be increased as the reaction proceeds. 

 Two suggestions have been made to account for the similar 

 state of affairs when cane-sugar is inverted simply by the action 

 of water at ioo°. Kullgren has shown that an acid is produced, 

 and as we know that the reaction is catalysed by H + ions, this 

 appears sufficient to account for the experimental results. Now 

 it is possible that the hydrolysis produced by invertase may 

 also be accompanied by the formation of acid, and, as the 

 activity of this enzyme is increased considerably by H + ions 

 in moderate concentration, the explanation of Victor Henri's 

 results may be found here. There is also another possibility 

 suggested by Mellor and Bradshaw in connection with inversion 

 of cane-sugar by water at ioo° — namely, that the glucose and 

 fructose as first formed may be in those modifications which 

 have the higher rotatory powers, and that only at a later 

 period, when equilibrium is attained, is the normal rotation of 

 glucose arrived at. If this is the case with invertase action, 

 it is obvious that if readings are taken of the change as it pro- 

 gresses in the tube of the polarimeter itself, these readings 

 will indicate a higher concentration of inverted sugar than 



