ENZYMES AS SYNTHETIC AGENTS 489 



stages of the hydrolysis, by various antiseptics used in the 

 course of his investigation. If the same enzyme was responsible 

 for both stages of the hydrolysis, then the change in velocity 

 in the two stages produced by the addition of the reagent 

 should be proportionately the same, but it was very far from 

 being so. Guided by this clue he subsequently succeeded in 

 isolating from hemp seed and from other sources extracts of 

 the two enzymes which were each strictly limited in their 

 activity to one stage of the hydrolysis. This separation had 

 proved to be possible owing to the fact that while ereptase is 

 readily soluble in water, the endo-peptase present with it is 

 practically insoluble in distilled water but readily soluble in 

 solutions of sodium chloride. 



The importance of these investigations from our present 

 point of view is obvious ; everything points to the complex 

 series of changes which ultimately effect the conversion of a 

 protein into an amino-acid, occurring under the action of a 

 series of enzymes or groups of enzymes. In view of the fact 

 that of the animal enzymes, peptase acts with the greater 

 celerity on complex proteins, it should perhaps be regarded as 

 the first group of enzymes in the series, and the protein in its 

 decomposition would then come under the action of three 

 groups of enzymes successively : ! 



"Pepsin" "Trypsin" Erepiase 



or Ecto-peptase group. or Endo-peptase group. group. 



Protein — $► Albumoses. —> Peptones. -> Amino-acids. 



Clearly then, when an attempt is made to follow this series 

 of reactions with enzyme catalysts in the direction of synthesis, 

 it would seem advisable to attempt to follow these steps in 

 the reverse order. But the significance of ereptase has been 

 recognised only in comparatively recent times, and as the work 

 we shall have to consider in the succeeding section has been 

 carried out with the other enzymes of the series, the starting 

 point for the synthesis has been a vaguely defined admixture 

 of bodies instead of amino-acids of definitely known com- 

 position. 



In the case of the plant, the question is at present com- 

 plicated by the incompleteness of our knowledge of the amino- 



1 See Bayliss, Nature of Enzyme Action, 2nd ed. p. 115. It is as yet 

 impossible, however, to correlate with any certainty this series of three enzyme 

 groups with the phenomena of proteoclastic digestion in the plant. 



