NATURE OF ENZYMES 40 



enzymes. One of the most important of these is the difference in the 

 susceptibility to poisons of enzymes and cells. ^ Strengths of certain 

 antiseptics that will either destroy or inhibit the action of living cells, 

 such as alcohol, ether, salicyhc acid, thymol, chloroform and toluene, 

 will harm free enzymes in solution little or not at all. This fact has 

 been of great assistance in distinguishing between the action of en- 

 zymes and of possible contaminating bacteria in experimental work. 

 Although this difference between enzymes and cells is characteristic, 

 it does not finally decide that the cell actions are not enzyme actions, 

 for it may well be that the poisons act chiefly by altering the physical 

 conditions of the cell so that diffusion is interfered with, thus seriously 

 interfering with the exchange of cleavage products between different 

 parts of the cell, and checking intracellular enzyme action, which we 

 shall see later requires free diffusion of the products for its continuance. 

 At the very least, however, we may look upon the intracellular en- 

 zymes as the most important known agents of cell metabolism, and 

 consequently of all life manifestations, and the changes they undergo 

 or produce in pathological conditions must be fully as fundamentally 

 important as is their relation to physiological processes. It therefore 

 becomes necessary for us to consider carefully — 



'THE NATURE OF ENZYMES AND THEIR ACTIONS 



Since up to the present time no ferment has been isolated in an absolutely pure 

 condition we are entirely unfamiliar with their chemical characters, and conse- 

 quently are obUged to recognize them solely by their action. As far as we know, 

 true enzymes never occur except as the result of cell life — they are produced with- 

 in the cell, and increased in amount b}^ each new cell that is formed, and, further- 

 more, they are present in every living cell without exception. As the same facts 

 are equally true of the proteins it is natural to associate the enzymes with pro- 

 teins, and so explain the importance of the proteins for ceU life.^ If enzymes are 

 obtained in any of the usual ways from animal cells or secretions they are always 

 found to give the reactions for proteins, even if repurified many times. But it 

 is well known that whenever proteins are precipitated the other substances in 

 the solution tend to be dragged down by the colloids, and it is possible that the en- 

 zymes are merely associated with the proteins in this way. Furthermore, enzymes 

 are known to become so closely attached to stringy protein masses, such as fibrin 

 and silk, that they cannot be removed by washing. Some have claimed that they 

 have secured active preparations of pepsin and invertase that did not give protein 

 reactions and contained very little or no ash or carbohydrate ; but it has so far been 

 impossible to secure trypsin free from protein, and diastase seems to be certainly of 

 protein nature. Davis and Merker^ find that the more pepsin is purified the more 



1 See discussion by Vernon, Ergebnisse d. Physiol.. 1910 (9), 234. 



- It would not be profitable to discuss fully all the various theories and 

 hypotheses that have been advanced, but the reader is referred to the following 

 chief compilations of the entire subject: Oppenheimer, "Die Fermente und ihre 

 Wirkungen," Leipzig; BayHss, "The Nature of Enzyme Action," Monographs on 

 Biochemistry, London; Stern, "Physico-chemical Basis of Ferment Action," in 

 Oppenheimer's "Handbuch d. Biochemie," Vol. 4, pt. 2; Samueley, "Animal Fer- 

 ments," ibid, Vol. I; A. E. Taylor, "On Fermentation," Univ. of California I\ibUca- 

 tions; Euler, "General Chemistry of the Enzymes," translated by T. H. Pope, 

 New York, 1912. 



' Another important point is that the closest imitation of enzymes, Bredig's 

 'inorganic ferments," seem to owe their action to their colloidal nature. 



* Jour. Amer. Chem. Soc, 1919 (41), 221. 



4 



