CHEMISTRY. 285 



now not only of scientific interest, but also immediate economic impor- 

 tance because of its bearing upon the problems of food conservation. 

 The results already obtained, taken in conjunction with the studies 

 of the efficiency of the maize proteins in human nutrition, carried out 

 in these laboratories at the same time, though independently of the 

 grant from the Carnegie Institution of Washington, have already 

 proven useful in support of the movement for a larger use of maize 

 as human food. 



Progress has also been made upon two of the problems referred to 

 in previous reports — the influence of hydrogen-ion concentration upon 

 the activity of the different amylases, and the relationship between 

 amylolytic and proteolytic activity in enzyme preparations from the 

 pancreas. 



The use of the Clark cell and rocking electrode has resulted in a much 

 sharper definition of the hydrogen-ion optimum for pancreatic amylase 

 than has previously been established and has confirmed our earlier 

 determination of the optimum for malt amylase. As regards the influ- 

 ence of hydrogen-ion concentration upon its activity, the amylase of 

 Aspergillus oryzcB bears much more resemblance to that of malt than 

 to that of the pancreas. The results of this comparative study are best 

 summarized by means of tables and curves rather than by such dis- 

 cussion as is feasible in the present report. 



In the method developed in this laboratory and frequently employed 

 here during the past seven years for the purification of pancreatic amy- 

 lase, a high-grade pancreatin is extracted with 50 per cent alcohol, the 

 filtrate precipitated with alcohol-ether mixture, and this precipitate 

 dissolved in water and precipitated with absolute alcohol, then redis- 

 solved and dialyzed in 50 per cent alcohol containing maltose to retard 

 deterioration, and finally precipitated by adding to the solution an 

 equal volume of a 1 : 1 alcohol-ether mixture. During the dialysis there 

 settles out in the dialyzing sacs some material which, originally soluble 

 in 50 per cent alcohol, has now become insoluble in the same solvent, 

 apparently as the result of the intervening precipitation in alcohol of 

 higher concentration. This by-product has little if any diastatic power, 

 but shows even higher proteolytic activity than does the final amylase 

 preparation. In fact, it is apparently the most active protease known, 

 and is worthy of much further investigation. 



In the course of our attempts to find whether the amylase and pro- 

 tease activities of the final product obtained by the method just out- 

 lined are due to separable substances, we have frequently substituted 

 for the usual final step a further fractionation, precipitating first 

 with a mixture of two parts of alcohol to one of ether, after which a 

 second precipitate was obtained by adding more ether. The amy- 

 lolytic activity of the first precipitate was usually lower than that of 

 the second, but the latter was not more active than our previously 



