GENERAL CHARACTERISTICS OF THE ENZYMES 205 



substances of which perhaps one is active or, perhaps, many. Could 

 we discover any chemical resembling invertase in its solubilities and 

 in its sensitiveness to temperature and so forth, and possessing the 

 action of invertase, we might be inclined to claim an identity between 

 the two and then analysis would give us a criterion of the purity of any 

 given invertase preparation. But at present we have no such criterion, 

 and we cannot say whether a given preparation of invertase is a single 

 or a multiple preparation, or whether it contains 99 per cent, of inver- 

 tase and 1 per cent, of impurities or, on the contrary, 1 per cent, of 

 invertase and 99 per cent, of impurities. 



In this connection the properties and peculiarities of invertase may 

 be regarded as illustrative of the peculiarities which distinguish nearly 

 all of the enzymes. The same difficulties are encountered in the study 

 of each of the enzymes in turn. It might be imagined that the problem 

 of extracting an enzyme in pure condition from a crude preparation of 

 proved activity could be attacked in a manner analogous to that 

 employed in the original discovery of radium; by employing a variety 

 of precipitant s and solvents to fractionate the crude preparation, reject- 

 ing the inactive and retaining the active fraction in each successive 

 stage of the process. Unfortunately, however, it is found that almost 

 every chemical procedure which we may employ results in some loss 

 of activity by the enzyme. If a fraction of the original crude pre- 

 paration be precipitated out from the rest it may be found, for example, 

 to contain an amount of active ferment corresponding to fifty per cent, 

 of the amount which was present in the crude preparation, while the 

 residue, after the separation of the precipitate, may be found to contain 

 none of the ferment whatever. In this way successive processes of puri- 

 fication involve successive losses, until the activity of the preparation 

 ultimately disappears altogether. It is for this reason that the more 

 impure preparations of the various soluble enzymes are usually more 

 active than those preparations which are relatively "pure," i. e., contain 

 a smaller variety of substances. 



We have referred to the fact that many different enzymes may be 

 mistakenly regarded as one if they chance to possess a common action. 

 As an illustration of how an enzyme regarded as a single chemical 

 individual may become, with increased acquaintance, recognized as 

 multiple, we may cite the Trypsins : enzymes which have this in com- 

 mon that they hydrolyze proteins and peptones in faintly alkaline 

 solutions. Until recently no means of distinguishing between dif- 

 ferent trypsins were known, and trypsin was tacitly assumed to be 

 one ferment and only one. Now the investigations of Emil Fischer 

 and of Abderhalden have shown us that there are many trypsins, which 

 differ from one another in, the relative ease with which they attack 

 different peptide-linkages. 



The enzymes are, as a rule, destroyed, or, at least, inactivated by 

 high temperatures. But this is by no means a rule without exceptions. 



