ENZYMES. 49 



The aqueous solutions can be kept at low temperatures for a long time 

 after the addition of toluene or chloroform. 



In all these cases the enzymes are obtained strongly contaminated 

 with other bodies, especially by proteins. Only in exceptional cases is 

 it possible to free the enzyme solution from protein so that the solution 

 does not give the ordinary protein reactions. This is true for the solu- 

 tion of saccharase obtained from yeast by treatment with water; if 

 this is shaken with kaolin the protein is adsorbed by the kaolin while the 

 solution contains the enzymes. 1 



No enzyme has thus far been obtained in a perfectly pure form, 

 and the chemical constitution as well as structure is therefore unknown. 

 The enzymes probably belong to the colloids; if they themselves are not 

 colloids, they occur at least with colloids, from which they may be sepa- 

 rated only with difficulty, if at all. The enzymes are characterized by 

 the fact that they are readily taken up by finely divided substances 

 (inorganic precipitates, carbon, kaolin, infusorial earth and other col- 

 loids such as alumina, iron hydroxide, proteins 2 ). This process may 

 act selectively, as from a solution certain enzymes can be taken up and 

 others not at all, or only to a slight extent (HEDiN, 3 MICHAELIS and 

 EnRENREiCH 4 ). The adsorption process is more or less irreversible 

 and differs in this from the adsorption of crystalloid substances. Still 

 the trypsin and rennin adsorbed by charcoal can be to a slight extent 

 expelled from the charcoal by means of other adsorbable substances such 

 as casein and albumin (HEDIN) . 5 Rennin taken up by charcoal can to 

 a very slight extent be set free by the addition of glucose (HEDIN) and 

 saccharase adsorbed by charcoal can be set free by cane-sugar (ERIKS- 

 SON) . 6 As we will learn below, the adsorbed enzyme is inactive. The 

 so-called shaking inactivation of enzymes or the loss in activity of enzymes, 

 which occurs on shaking their solution seems to be due to an adsorp- 

 tion of the enzyme when it is either taken up by the precipitate 

 formed on shaking (ABDERHALDEN and GUGGENHEIM) or is concentrated 

 at the surface between the solution and the froth (S. AND S. SCHMIDT- 

 NIELSEN) . 7 These latter found the inactivation of rennin by shaking 

 was regained if the froth was allowed to subside. 



All enzymes lose their specific action on sufficiently heating their 



1 Michaelis, Bioch. Zeitschr., 7, 488 (1907). 



2 Dauwe, Hofmeister's Beitrage, 6, 426 (1905). 



3 Bioch. Journ., 2, 112 (1907). 



* Bioch. Zeitschr., 10, 283 (1908). 



5 Bioch. Journ., 2, 81 (1906); Zeitschr. f. physiol. Chem., 63, 143 (1909). 

 6 Hedin, ibid., 63, 143 (1909); Ericksson, ibid., 72, 313 (1911). 

 7 Abderhalden and Guggenheim, Zeitschr. f. physiol. Chem., 54, 352 (1907); S. and 

 S. Schmidt-Nielsen, ibid., 68, 317 (1910) which also contains the literature. 



