1913.] 



Studies on Enzyme Action. 



593 



When the amounts of ethereal salt and enzyme were kept constant the 

 amount hydrolysed decreased as the solution was diluted. 



Thus in 5 c.c. M/10 solution +0 c.c. water 62'5 per cent, was hydrolysed 



2 „ 59-4 



5 „ 61-2 

 10 „ 53-5 

 20 „ 40-1 

 40 „ 15-4 „ 



Thus everything tends to show that lipase is very sensitive to the action 

 of acids, though acids are produced by its action. Its inferiority as a 

 hydrolyst of ethereal salts other than fats and its power of hydrolysing the 

 complex natural glycerides readily, apparently to an almost unlimited extent, 

 would seem to be due to the fact that the acids that are liberated from fats 

 are scarcely if at all soluble in water and very weak. 



Mode of Action of Lipase. — The argument previously put forward (Part II) 

 in explanation of the activity exercised by lipase is as follows : — 



'•' The ethereal salts which are hydrolysed under the influence of lipase are 

 all compounds of the type E'.CO.OX'. Since E' and X' may be varied 

 within wide limits, it cannot well be supposed that the selective action of 

 the enzyme is exercised with reference either to E' or X' ; consequently, the 

 controlling influence must be attributed to the carboxyl radicle (CO.O) : the 

 enzyme must be so constituted that it can ' fit itself to this group.' 



" Our experiments have led us to form the provisional hypothesis that the 

 hydrolysis of the ethereal salt by Lipase involves the direct association of the 

 enzyme with the carboxyl centre, and that such association may be prevented 

 by the ' hydration ' of this centre : consequently, that those salts which are 

 the more attractive of water will be the less readily hydrolysed." 



The behaviour of soluble ethereal salts, especially the fact they are the 

 less readily acted upon the more soluble they are and the stronger the acid 

 from winch they are derived, may be better accounted for, however, by 

 assuming not that the carboxylic centre of the ethereal salt is hydra ted and 

 that therefore the association of the enzyme with this centre is prevented : but 

 that salt and enzyme are the more kept apart, through the agency of water, 

 the more soluble the salt is, because the salt is the more attracted by the 

 water ; and that the enzyme is the more interfered with, through the fixation 

 of acid, the stronger the acid. 



It remains to account for the special affinity of lipase to fats. Owing to 

 the fact that it acts on carboxylic ethereal salts in general, it cannot be 

 supposed that it has any special attractive influence over the molecule of the 

 hydrolyte as a whole, such as is pictured in the previous communication as 



