THE Ph'i\rfpLi:s OF Kx/.VMi: AcTioy 57 



ethyl alcohol, butyric acid, etliyl l)utyrati', and water exists. -wIk'h the 

 chaiijro will stop, i. e., eqiiUibriKin is cstubiishcd. The time that 

 would be required for this reaction to occur at room temperature 

 would be extremely long, the change being hardly noticeable, but in 

 the presence of a catalytic agent the reaction goes on much more 

 rapidly. Catalytic agents, therefore, merely hasten reactions which 

 would go ou without them, and they do not initiate or change the na- 

 ture of chemical reactions at all. AVhen equilibrium is established, the 

 reaction stops and the en/ymc has notliing more to do. Furthermore, 

 and this is a recently a])preciated fact, enzymes will hasten synthesis 

 just as well as they hasten catalysis. Croft Hill first showed that 

 maltase would synthesize glucose into maltose ; Kastle and Loevenhart 

 soon after established the synthesis of ethyl butyrate under the in- 

 fluence of lipase. Taylor '^ first synthesized one of the normal 

 body fats, triolein, by the action of lipase (from the ca.stor-oil bean) 

 iipon oleic acid and glycerol. Successful synthesis of fats by pan- 

 creatic lipase is described by Lombroso.'^ It may seem improbable at 

 first sight that the synthesis of proteins can be accomplished by 

 enzymes, as is the relatively very simple synthesis of carbohydrates 

 and fats, but the improbability disappears when we recall that the 

 jjroducts of protein cleavage are reconverted into body proteins after 

 absorption from the intestines. Proteins manifestly are synthesized 

 and we have not a little reason to believe that this is accomplished by 

 enzymes, presumably by a reversal of their action in the establishment 

 of equilibrium. Taylor ^ was able to synthesize protamin, one of the 

 simplest proteins, by the action of trypsin upon its cleavage products, 

 and it has been found that the addition of proteolytic enzymes to solu- 

 tions of pure albumose leads to the formation of a jelly-like, insoluble 

 protein substance, ' ' plastein, ' ' which seems to be the effect of a reversed 

 action on the part of the enzymes." Another well known synthetic ac- 

 tion that seems to be due to reversible ferment action is the formation 

 of hippuric acid from benzoic acid and glycocoU in the kidney; the 

 formation of glucose into glycogen and its reformation are also prob- 

 ably both accomplished by one and the same enzyme acting reversibly. 

 Other reversible reactions less closely related to animal cells liave also 

 been described. 



The reversible nature of enzyme action explains many problems of 

 metabolism, and makes the whole field much clearer. The following 

 consideration of the newer understanding of fat metabolism on this 



6 Univ. of California Publications (Pathology), 1004 (1), 33. 



7 Arch, di farmacol., 1012 (14), 420. 

 8. Tour. Biol. Cliem.. 1000 (r,), 381. 



See Micheli, Arch. ital. biol., 1000 (46). 185: Lcvcnc aiul Van Slykc. r.iocliom. 

 Zeit, 1008 (13), 4.58; Tavlor, .Tour. Biol. Cheni.. 1000 (5), .300; Gay and Robert- 

 son, ibid. 1912 (12), 233; Abderhalden. Fermentforsch., 1014 (1), 47; v. Knaffl- 

 Lenz and Pick, Arch. exp. Path., 1013 (71), 206, 407. 



