ARTICLES 407 



lipase show the characteristics of protein, while the invertase 

 described by Nelson (1914) is a carbo-hydrate phosphoric acid 

 complex containing about i per cent, nitrogen in the form of 

 protein. The problem of preparing pure enzyme is a very 

 difficult one, and as Falk states (1918) : "Asa result of the 

 complex nature of the protein or other molecule which includes 

 the enzyme or with which the enzyme may be associated, the 

 problem of isolating pure enzyme must wait for the solution of 

 the problem of the isolation of pure proteins possessing the 

 properties which they exhibit in living matter, using the term 

 living to include also matter showing the action of enzymes." 



Initiation of Reaction. — If enzymes are to be considered as 

 catalysts, they should be able as such to hasten but not to 

 initiate reactions. It has been observed that starch solutions 

 on keeping pass into dextrin or sugar, and it has also been found 

 that the increase in electrical conductivity which occurs when 

 trypsin acts on ammonium caseinogate will take place slowly 

 if the caseinogate is left to itself. The fact, however, cannot be 

 ignored that such an eminent chemist and physicist as J. J. 

 Thomson considers it possible that a reaction may be begun by 

 an enzyme, and indeed the recent work of McGuigan (1919) on 

 ptyalin would tend to support Thomson's hypothesis at least 

 with regard to that enzyme. 



Where the process catalysed is one of hydrolysis, it may be 

 assumed that it is slowly taking place as a result of the H and 

 OH ions in the water of which the solution may be made ; but 

 the difficulty of recognising extremely slow reaction is very 

 great. No work on this point appears to have beepi done in 

 relation to oxidation processes which are known to be accelerated 

 by enzymes. 



Relation of Enzymes to Products of Reaction. — In true cata- 

 lytic action the catalyst should appear unchanged at the end of 

 the reaction, and in its original quantity, but in the case of 

 enzymes this is not ahvays demonstrable. In 19 10 Starkenstein 

 and subsequently Bayliss satisfied themselves that enzymes 

 could be obtained unchanged ; but the facts that enzymes tend to 

 decay spontaneously when much diluted and that reaction 

 may take place slowly even without enzymes give much 

 experimental difficulty and may lead to erroneous conclusions ; 

 such as those of Bradley, who found (1910) that the amount of 

 triolein hydrolysed by lipase was in proportion to the amount 

 of enzyme present. If the enzyme itself played any part in 

 the final state of the reaction, it is to be presumed that the 

 addition of more enzyme would change the amount of the 

 products. The work of Bayliss in 191 3 shows that this is not 

 so. Reference to further work on this subject will be made 

 when dealing with " Equilibrium " and " Reversibility." 



