CHEMICAL CHANGES IN LIVING MATTER. FERMENTS 185 



VELOCITY OF TRYPSIN REACTION 



N 



6 c.c. 8 per cent, caseinogen + 2 c.c. AmHO + 2 c.c. 2 per cent. 



trypsin at 39 C. 



1st 10 minutes K = 0-0079 



2nd 0-0046 



3rd 0-0032 



4th 0-0022 



5th 0-0016 



7th 0-0009 



&c. &c. 



The cause of this rapid diminution in the velocity of change is 

 probably complex. One factor may be an auto- destruction of the 

 ferment, which is known to occur in watery solution. That this 

 is not the only, or even the chief, factor involved is shown by the 

 fact that, when the action of trypsin on caseinogen has apparently 

 come to an end, it may be renewed by further dilution of the mixture 

 or by removal of the end-products of the action by dialysis. It is 

 evident that, in this retardation of the later stages of ferment action, 

 the end-products are concerned in some way or other, and the retarda- 

 tion can be augmented by adding to the digesting mixture the boiled 

 end-products of a previous digestion. The retarding effect of the 

 end-products resembles in many ways that observed in a whole series 

 of reactions which are known as reversible. 



As an example of such a reaction we may take the case of methyl acetate 

 and water. When methyl acetate is mixed with water, it undergoes decom- 

 position with the formation of methyl alcohol and acetic acid. On the other 

 hand, if acetic acid be mixed with alcohol, an interaction takes place with the 

 formation of methyl acetate and water. These changes are represented by the 

 equation : 



MeC 2 H 3 O 2 + HOH ;= MeOH + HC 2 H 3 O 2 . 

 methylacetate water methylalcohol acetic acid 



Each of these changes has a certain velocity constant, and, since they are in 

 opposite directions, there must be some equilibrium point where no change will 

 occur, and there will be a definite amount of all four substances present in the 

 mixture, namely, water, alcohol, ester, and acid, This equilibrium point can 

 be shifted by altering the amount of any of the four substances. Thus the inter- 

 action of methyl acetate and water can be diminished to any desired extent 

 by adding to the mixture the products of the interaction, namely, methyl alcohol 

 and acetic acid. 



There is evidence that some of the ferment actions are reversible. 

 Thus maltase acts on maltose with the formation of two molecules of 

 glucose. If the maltase be added to a concentrated solution of glucose, 

 we get a reverse effect, with the production of a disaccharide which 

 has been designated as isomaltose or revertose. To this reverse action 

 may be due a certain amount of the retardation observed in the action 



