CHAPTER XVII 

 THE ENZYMATIC SYNTHESIS OF PROTEINS 



1. The Reversion of the Hydrolysis of Proteins by Pepsin and 

 Trypsin. — In "typical" catalysed reactions (Cf. previous Chap- 

 ter, section 1), since the equilibrium of the system is not shifted 

 by the catalysor and the point of equilibrium is determined by 

 the ratio of the velocity-constants of the forward and the opposed 

 reactions, both velocity-constants must be multiplied to an equal 

 degree by the catalysor; in other words, if under given conditions 

 a point of equilibrium exists at which an appreciable proportion 

 of the substrate remains unaltered, then, under such conditions, 

 the pure products (unmixed with substrate) are not in equilibrium 

 and must be tending to restore the substrate, and this tendency 

 must be increased by the presence of the catalysor in question. 



As this fact became generally appreciated, following its ex- 

 perimental verification in a large number of non-fermentative 

 catalytic reactions, and as the belief gained ground that the 

 ferments were to be regarded as "typical" catalysors, it was 

 anticipated that fermentative reversions might be accomplished, 

 that is the synthesis of substances which are normally hydrolysed 

 (or otherwise altered) by enzymes, through acting upon the 

 products of hydrolysis with the same enzymes. This theoretical 

 anticipation was first experimentally realized by Croft Hill (31) 

 (32) in the fermentative synthesis of isomaltose (16) (2) (3) 

 from glucose, and has since been realized in the fermentative 

 synthesis of polysaccharides, fats, and proteins by various investi- 

 gators (7) (34) (26) (8) (66) (67) (69) (70) (47) (48) (9) (51) (52). 



In order to make clear the conditions under which such re- 

 versions occur it will be well to consider in some detail the funda- 

 mental experiment performed by Croft Hill. 



The hydrolysis of maltose (or of isomaltose) is represented 

 by the equation : 



(A) Ci2H220n + HoO ^ 2 CeHisOe; 



the reversion is represented by the equation : 



(B) 2 CeHiaOe -> Ci2H220n + H2O. 



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