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Tryptase on the other hand is regarded as being capable 

 both of acting in neutral, slightly acid, or alkaline solutions, and 

 of carrying the digestive hydrolysis as far as the production of 

 polypeptides and amino-acids. Recent work suggests that this 

 difference in the extent to which hydrolysis is carried is not 

 really significant, but that, if sufficient time be allowed, amino- 

 acids will be found among the products of peptic digestion. 1 



Ereptase activates hydrolysis from the point at which peptase 

 is usually regarded as ceasing to act. Acting upon albumoses 

 and peptones, it converts them, apparently completely, into 

 polypeptides and amino-acids. 



In plants these three groups of enzymes cannot be separated 

 by any reference to their distribution. The peptic type of 

 enzyme seems to be chiefly represented in the secretions of 

 insectivorous plants, such as Nepenthes. These enzymes Vines 

 terms ecto-peptases to distinguish them from the internally held 

 and controlled enzymes of similar catalytic activity in protein 

 hydrolysis, such as the endo-peptase present in yeast. 



The enzymes which are usually regarded as active in re- 

 converting the deposits of aleurone grains within the seed into 

 amino-acids were first described as tryptic, because their activity 

 resulted in the formation of amino-acids from the proteins 

 hydrolysed. Vines in a series of papers 2 has built up a strong 

 case for interpreting all cases of so-called " tryptic " digestion in 

 plants as due in reality to two enzymes, acting on two different 

 stages. The first stage from protein to peptone is regarded as 

 due to the catalytic action of a peptase — an ecto-peptase in the 

 excretion of Nepenthes capable of acting in the presence of 

 hydrochloric acid or organic acids, but inactive in neutral or 

 alkaline solutions, and an endo-peptase in the tissues of the 

 seedling and elsewhere, incapable of action in the presence of 

 hydrochloric acid. The second stage from peptone to amino- 

 acid is regarded as due to the catalytic activity of a widely 

 distributed ereptase capable of acting in either acid, neutral or 

 alkaline solution. 



Vines was led to suspect the existence of these two stages by 

 noticing the different effect exerted upon the rate of the two 



1 Lawrow, Zeit.filr Physiol. Chem. 26, p. 513. 



3 Vines, Annals of Botany, xi. p. 563, xii. p. 545, xv. p. 563, xvi. p. I, xvii. 

 p. 237, xviii. p. 289, xix. pp. 149 and 171, xx. p. 113, xxii. p. 103, xxiii. p. I, xxiv. 

 p. 215. 



