io SCIENCE PROGRESS 



reversible nature of these reactions and assume that they pro- 

 ceed to completion. 



In such cases the rate at which the change proceeds will 

 be, at any moment, proportional to the amount of unaltered 

 substrate present at that moment. A simple application of the 

 calculus shows us that the time course of the reaction will there- 

 fore form a logarithmic curve, when put into the graphic form. 



What is the nature of the corresponding curve when 

 enzyme actions are concerned? Several cases have already 

 been investigated; but it can only be regarded as somewhat 

 unfortunate that the first of such reactions to be completely 

 analysed, chiefly by Victor Henri, turns out to be an anomalous 

 one. I refer to the action of invertase on cane-sugar. When 

 the values of the velocity constant in this instance are calculated 

 by application of the unimolecular formula to the experimental 

 data, it is found that the values so found steadily increase, 

 instead of remaining the same all through. In nearly all other 

 examples worked out up to the present time the corresponding 

 values steadily decrease. Such are maltase and lactase (E. F. 

 Armstrong), emulsin (Tammann), lipase (Kastle), and trypsin 

 (by myself). Amylase is stated by some to follow the same law 

 as invertase. 



In the greater number of cases there are, then, some 

 influences at work which either diminish the amount of enzyme 

 acting or in some way make it less active. The chief cause 

 seems to be the increasing concentration of the products of 

 reaction, since by adding these, or certain of them, it is found 

 that the reaction is slowed. There are several possible ways in 

 which this effect may be produced. In the first place there is 

 some evidence that there is a kind of combination taking place 

 between the enzyme and certain of the products of its action ; 

 this would result in a part of the enzyme being withdrawn 

 from participation in the reaction. In the second place, as 

 insisted on by Moore, the reversible nature of these reactions 

 has not been sufficiently taken into account; even where the 

 reaction appears to proceed to completion it is probable that 

 this means that the equilibrium point is very near one end, and 

 the tendency for the reaction to run in the opposite direction 

 will show itself more and more as this equilibrium point is 

 approached. In the cases of invertase and emulsin investigated 

 by Visser from this point of view, it was found that the 



