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 sub- 

 stances 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. Proteins are being continually broken down into 

 urea, carbon dioxide, and water; yet to split proteins even as far as the 

 amino-acid stage requires prolonged action of concentrated acids or 

 alkalies, or super-heated steam under great pressure. But all the time 

 in the cell innumerable equally difficult changes are going on at once, 

 within its tiny mass, always keeping the resulting heat within a frac- 

 tion of a degree of constant, and the resulting products within narrow 

 limits of concentration. We have already indicated the means used 

 to keep the concentration of the cell products within safe limits; 

 namely, the processes of diffusion and osmosis and their modification 

 by the cell structure. The forces that bring about the chemical reac- 

 tions 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 equallj^ unknown. 

 When the only enzymes that were known were limited to those se- 

 creted from the cell, and found free in fluids, such as pepsin and tryp- 

 sin, 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 contents able to produce the same 

 changes in carbohydrates that the cells themselves did, proved the ex- 

 istence within living cells of enzymes similar to those excreted by cer- 

 tain cells, and substantiated the belief of their existence that had 

 become general before it was thus finally corroborated. Growing out 

 from this and subsequent experiments has come a larger and larger 

 amount of evidence that many of the chemical activities of the cells 

 are due to the enzymes they contain, until now the point is reached 

 where one may rightfully ask if cell life is not entirely a matter of 

 enzyme activity. There are certain facts, however, which seem to in- 

 dicate that there are some essential differences between cells and 



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