384 



Studies on Enzyme Action. 



Appendix. (August 14, 1906.) 



Since the foregoing account was written, a large number of experiments 

 have been made with the object of contrasting animal lipase with vegetable 

 lipase. We have been led gradually to recognise that in the case of the 

 former especially, if an effective comparison is to be made between ethereal 

 salts, it is an essential condition of success that the substances compared be 

 in solution. We were led to this conclusion in the first place by observing 

 in certain experiments, in which the materials were only partially dissolved, 

 that ethylic propionate was more acted upon than was either the acetate or 

 butyrate ; but when solutions of equivalent quantities of the three salts 

 were acted upon by liver lipase, the acetate proved to be the most and the 

 butyrate the least stable. We need scarcely point out that this circumstance 

 renders a strict comparison of ethereal salts which are only very slightly 

 soluble in water a difficult matter ; moreover, it must be taken into con- 

 sideration in connection with our earlier experiments. Probably it is on 

 this account also that the liquid expressed both from the liver and the 

 pancreas acts so slowly and to so slight an extent on natural fats and oils. 

 With these agents, however, it appears to be impossible to secure anything 

 approaching to the complete emulsification of fats which is readily effected 

 by the residue of castor oil seeds ; indeed, at present we are inclined to 

 attribute the extraordinary activity of the seed residue to its emulsifying 

 power rather than to any inherent superiority of the enzyme as a lipoclast ; 

 but it should be mentioned that any treatment which renders the enzyme 

 in the seed residue inactive also destroys the emulsifying power of the 

 material.* All attempts which we have made to overcome the difficulty 

 referred to by dissolving the fat or oil in neutral liquids such as toluene or 

 ether and then violently agitating the solution with liver juice have proved 

 unsuccessful — such treatment having served oidy to destroy the enzyme. 



In confirmation of the statement already made with reference to the 

 remarkable and, as we believe, significant difference in behaviour of the 

 allied salts, ethylic succinate, malate and tartrate, the following results may 

 be quoted which were obtained by digesting solutions of equivalent quantities 

 of the three compounds with liver lipase. The figures represent the quantity 

 of alkali required to neutralise the liberated acid ; at the end of the experi- 

 ment the succinate was practically all hydrolysed : — 



* It is not improbable that the increased activity of pancreatic juice (from a'Pawlow 

 fistula) in presence of bile salts, to which Magnus has recently called attention (' Zeits. 

 Physiol. Ohem.,' 1906, vol. 48, p. 376), is due to the promotion of emulsification by 

 the salt. 



