CHEMISTRY. 387 



tion which the enzyme undergoes in the aqueous dispersion in which 

 it acts. The experimental evidence mentioned in our last report has 

 been extended by further work during the intervening year, which 

 has shown that the inactivation of the enzyme by copper and its 

 reactivation by amino acid, and the protection afforded by the amino 

 acid against the deterioration which the enzyme undergoes in water, 

 are processes in which time and temperature exert a marked in- 

 fluence. Some of these results have been prepared for publication, 

 and further experiments, particularly with reference to the influence 

 of temperature, are planned for the coming year. The results already 

 obtained afford striking evidence that deterioration of the enzyme with 

 rise in temperature is retarded by the presence of an amino acid such as 

 glycine. Presentation of the data in quantitative terms is deferred 

 until after the completion of further experiments. 



In the experiments above described six different mono-amino acids 

 have been employed. Another series of experiments has been carried 

 on to test the influence of four amino acids of more complicated struc- 

 ture, namely arginine, histidine, tryptophane, and cystine Since 

 these amino acids, or several of them, interfere with the determination 

 of the reducing sugar formed by the action of the enzyme upon the 

 starch, the method w^hich we have commonly employed for the de- 

 termination of enzymic activity of an amylase preparation based upon 

 the measurement of its saccharogenic power, was here replaced by a 

 method in which the amyloclastic activity of the enzyme was measured 

 instead. Tests with two of the mono-amino acids previously tested, 

 glycine and phenylalanine, showed that the two methods were inter- 

 changeably adapted to the demonstration of their favorable influence 

 upon the enzymic activity of the amylase. For this series, the purified 

 pancreatic amylase preparation was chosen, as being the form of en- 

 zyme best adapted to the purpose of these experiments. Arginine 

 and cystine were found to resemble the mono-amino acids in their 

 favorable influence upon the activity of this enzyme ; whereas no such 

 favorable influence was shown by histidine or tryptophane. 



If the favorable influence be conceived as a direct accelerating effect 

 exerted by the amino acid in consequence of its own chemical struc- 

 ture, it would seem logical to refer this effect to the presence of the 

 a-amino group as the one common feature of all these amino acids. 

 The failure of histidine and tryptophane to show favorable results 

 would thus be explainable upon the ground that their heterocycles 

 must have exerted an inhibitory influence upon the enzjTne sufficient 

 to offset the favorable influence of their a-amino group. 



On the alternative hypothesis that the amino acid exerts its favorable 

 influence by retarding the deterioration of the enzyme in the aqueous 

 dispersion in which it acts, the differing effects of certain amino acids 

 is readily explainable if the enzyme be regarded as essentially a pro- 

 tein substance or as containing protein as an essential constituent. 



