CATALYSIS AND ENZYMES 



319 



particular temperature. Neither the optimum nor the lethal temperature is a fixed 

 point ; a short exposure to a high temperature may not kill an organism, while a 

 longer exposure to a rather lower one may be fatal. 



Some of the earlier workers with enzymes seem to have regarded the optimum temperature 

 of enzyme action as something mysterious, even indicating " vital action." We see that it is 

 merely the expression of the sensitiveness of the colloidal arrangements of the enzyme system 

 to rise of temperature, and is not confined to enzymes, but may be shown by inorganic colloids. 



FIG. 85. INTERIOR OF VAN'T HOFF'S PRIVATE ROOM IN THE OLD LABORATORY 

 AT AMSTERDAM (1877-1891). On the left of the photograph is a window, 

 in front of which stands a table. This table was van't Hoff s chief work- 



(Reproduced by the kindness of Prof. Ernst Cohen 

 of the van't Hoff Laboratory, Utrecht. ) 



There is one practical point in connection with the great acceleration of enzyme 

 action by rise of temperature. It is often necessary to stop a reaction at a 

 particular stage ; this must not be done, if any accuracy is required, by raising 

 the sample to the boiling point. However quickly this can be done in practice, 

 the enzyme is not immediately destroyed, and during its short life, it acts with 

 great energy, owing to the considerable rise in temperature. If dilution i 

 permissible, the sample may be allowed to fall, drop by drop, into boiling water. 

 Better, if the addition of chemical substances is immaterial, as is usually the 

 case, mercuric nitrate may be added, which immediately precipitates and destroys 

 the enzyme. 



