118 THE SO-CALLED INORGANIC ENZYMES 



form, as in the case of fibrin ferment precursor (pro-thrombase) 

 in oxalated plasma, or of pepsin from pure gastric juice. 



The investigations have shown that enzymes are not in all 

 cases proteids. Thus the purer preparations of pepsin and in- 

 vertase do not give the proteid colour tests. 1 In elementary 

 composition the enzymes do, however, resemble the proteids more 

 than any other class of bodies. In addition to being salted out, 

 or precipitated out like colloids, the enzymes are further shown 

 to be colloids by the fact that they do not diffuse through parch- 

 ment paper, or diffuse with great slowness. 



THE SO-CALLED INORGANIC ENZYMES OR METAL-SOLS 



It has already been repeatedly stated that the enzymes are 

 a particular class of the bodies known as catalysts, which modify 

 the conditions of a reaction. The enzymes differ from most of 

 the inorganic catalysts, however, in that they are colloids, and 

 to this certain of the differences in action between inorganic 

 catalysts and enzymes are due. 



The method of Bredig for obtaining, in the case of certain 

 metals, catalysts of inorganic nature in colloidal solution as 

 metal-sols is hence of high interest. These metal-sols have been 

 termed inorganic enzymes by Bredig from their close resemblance 

 in many respects to the enzymes produced by living cells ; but it 

 is questionable whether the use of such a term is justifiable, since 

 the properties of such colloidal solutions are only exaggerations, 

 probably on account of increased surface, of the action of the 

 finely divided metals when not in solution, and most of the reac- 

 tions destroying or removing the properties of such solutions may 

 be ascribed to the throwing of the metal out of solution or to 

 alteration of the active surface. 



We have no proof that the similar actions in the case of the 

 enzymes are due to similar causes. Also, we have no case where 

 these colloids act upon another colloid as in the case of enzymes, 

 nor of any hydrolytic action upon organic bodies caused by their 



1 In other cases it appears almost certain that either the enzyme is a com- 

 pound proteid or closely attached to one, for example, trypsin and thrombase. 

 Also the precipitate from gastric juice in the cold appears to be a compound 

 proteid according to recent observations of the Pawlow school. 



