MECHANISM OF METABOLISM 2ig 



will be formed. The same is true with enzymes, at least with some 

 enzymes. Maltase will decompose maltose into two molecules of 

 dextrose. In a concentrated solution of dextrose, however, maltase 

 will form maltose, or a similar sugar, isomaltose. Lipase is able to 

 produce fat from glycerin and fatty acids. A solution of albumose 

 with trypsin or pepsin gives a precipitate of a body which is more com- 

 plex than albumose and which gives the protein reactions. It is 

 believed by many physiologists that pepsin and rennet are the same 

 body. Under certain conditions, it has a dissolving power, under other 

 conditions it has the power to coagulate. 



The reversibility of enzymic action has given rise to much specula- 

 tion about assimilation and growth. It seems reasonable to suppose 

 that the cell forms its protoplasm from amino-acids by the reversed 

 action of proteolytic enzymes. In the same way, cellulose may be 

 formed from dextrose, fat from glycerin and fatty acids. Nearly all 

 phases of growth can be accounted for in this way. This is nothing but 

 theoretical speculation, and the only fact to support it is the reversi- 

 bility of certain enzymes. The conditions under which chemical reac- 

 tions take place inside of the cell are very largely unknown. There 

 are so many processes going on at the same time that it is absolutely 

 impossible at the present time to obtain a perfect understanding of all 

 these reactions. Thus, our knowledge of growth is largely based 

 upon analogy and speculation. 



GENERAL ENZYMIC CONSIDERATIONS 



Enzymes are produced only by living cells. After they are once 

 formed, they act like chemical compounds, independent of the cell 

 which produces them. Even the endo-enzymes follow only the law of 

 enzyme-action and are not influenced by the cell which contains them. 

 The enzymes are mostly influenced by their own products, and when 

 a certain yeast ceases to ferment sugar at the concentration of 8.5 

 per cent of alcohol, this means that the alcoholase of this yeast cannot 

 tolerate more than 8.5 per cent of alcohol. The inability of the cell 

 to regulate enzymic action may account for the fact that often a 

 culture produces an amount .of fermentation products sufficient to 

 kill all cells. This is observed in the lactic, acetic and alcoholic fer- 

 mentations, and, perhaps, occurs in many others. 



