CHAPTER II 

 ENZYMES 



EVERY cell is constantly accomplishing an enormous number 

 of chemical reactions of varied natures, at one and the same time ; 

 how many we do not know, but the score or more that we do 

 know to be constantly going on in the liver cell, for example, are 

 probably but a part of the whole. Furthermore, reactions take 

 place between substances that show no inclination to affect each 

 other outside the body, and proceed in directions that we find it 

 difficult to make them take in the laboratory. Sugar is being 

 constantly oxidized into carbon dioxide and water, a decomposi- 

 tion that requires high degrees of heat or powerful chemicals to 

 bring about in the reagent glass. Proteids are being continu- 

 ally broken down into urea, carbon dioxide, and water ; yet to 

 split proteids even as far as the amino-acid stage requires pro- 

 longed action of concentrated acids or alkalies, or superheated 

 steam under great pressure. 1 But all the time in the cell a 

 multitude of equally difficult changes is going on at once, 

 within its tiny mass, always keeping the resulting heat within 

 a fraction of a degree of constant, and the resulting products 

 within narrow limits of concentration. We have already indi- 

 cated the means used to keep the concentration of the cell prod- 

 ucts within safe limits ; namely, the processes of diffusion and 

 osmosis and their modification by the cell structure. The 

 forces that bring about the chemical reactions reside, we say, in 

 enzymes, although in so doing we only shift the attribute 

 formerly conceded to the cell, to certain constituents of the cell 

 whose nature and manner of action are equally unknown. 

 When the only enzymes that were known were limited to those 

 secreted from the cell, and found free in fluids, such as pepsin 

 and trypsin, the chemical changes that went on in the cell were 

 ascribed to its "vital activity." Buchner, by devising a 

 method to crush yeast cells, and finding the expressed cell con- 

 tents able to produce the same changes in carbohydrates that 

 the cells themselves did, proved the existence within living 

 cells of enzymes similar to those excreted by certain cells, and 



1 For a, fuller consideration of these phases of cell activity read Hofmeister, 

 " Die chemische Organisation der Zelle," Braunschweig, 1901. 



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