CHEMISTRY. 



339 



addition of amino acid to the digestion mixture were, in the present 

 series of experiments, as follows: 



Commercial pancreatin 



Purified pancreatic amylase 



Saliva 



Malt extract 



Purified malt amylase 



Commercial takadiastase 



Purified amylase of Aspergillus oryzse 



The most prominent result of this comparative study is the general 

 similarity of the data obtained for the four amino acids here reported 

 and the two whose effects were discussed in our previous report. Al- 

 lowing for divergences attributable to experimental error, it appears 

 that the effect of amino acid in facihtating the enzymic hydrolysis of 

 starch is similar, but not necessarily identical, for the different amino 

 acids thus far investigated; that it is somewhat greater for the purified 

 form of the enzyme than for the natural or commercial material in 

 which the enzyme is accompanied by other constituents of the tissue 

 or secretion in question; and that it is greater for the pancreatic and 

 salivary amylases than for the amylases of malt and of Aspergillus 

 oryzce. In general, the addition of a mixture of two amino acids gives 

 practically the same effect as would result from a corresponding con- 

 centration of one of them. Such experiments have been made with the 

 following mixtures: aspartic acid and asparagine, aspartic acid and 

 glycine, tyrosine and asparagine, phenylalanine and asparagine, alanine 

 and glycine. 



In all of the experiments, either with individual amino acids or with 

 mixtures, the substances to be tested have been neutralized before in- 

 troducing them into the digestion mixture, and repeated determinations 

 by the electrometric method have demonstrated that the influence of 

 the amino acid or acids upon the enzymic hydrolysis of the starch 

 is not, in our experiments, due to change of hydrogen-ion concentration. 



Some progress has been made in the study of the interesting ques- 

 tion whether the amino acid literally activates the enzyme or rather 

 protects it from deterioration or inactivation. The very rapid deterio- 

 ration of water solutions of pancreatic amylase, particularly when highly 

 purified, and the influence of the sodium chloride and secondary 

 phosphate (regularly used to activate this enzyme) in retarding the 

 deterioration have been noted in previous reports. Since the loss of 

 enzymic activity is only retarded and not entirely prevented by the 

 presence of these salts, it seemed not improbable that the favorable 



