308 



PRINCIPLES OF GENERAL PHYSIOLOGY 





certain incidental properties which distinguish them from the majority of inorganic 

 catalystsj but this is all that we are justified in asserting. 



It is interesting to note that Von Wittich (1872) had already come to the conclusion that 

 pepsin merely accelerates the action of hydrochloric acid on fibrin, but it is not quite dear 

 whether he intended to make the statement that enzyme actions in general are catalytic 

 actions, although it appears to be so. 



A name is often wanted for the substance on which an enzyme acts. No 

 satisfactory one has been suggested. " Hydrolyte " excludes all processes except 

 hydrolysis, " zymolyte " applies only to enzymes and excludes other catalysts, a 



suggestion of difference which 

 is to be deprecated. " Sub- 

 strate " is in very general 

 use ; it is rather an awkward 

 word in English, but will be 

 used in the following pages. 



To distinguish the differ- 

 ent enzymes, Duclaux sug- 

 gested adding the termination 

 " ase " to the name of the 

 substrate, thus "lactase" is 

 the enzyme which acts on 

 lactose. Certain old names, 

 such as " pepsin " and " tryp- 

 sin," are, however, still in use. 

 The termination " lytic " 

 has been used for a class of 

 enzymes acting on a group of 

 substances; a proteolytu- 

 enzyme is one that acts on 

 the proteins in general, and 

 includes pepsin and trypsiri. 

 Armstrong (1890) has justly 

 pointed out that "proteo- 

 lytic," in analogy with 

 " electrolytic," should mean 

 decomposition by means of 

 protein, not decomposition of 

 protein itself. To avoid this 

 misuse, the termination 

 " -clastic " was suggested, and 

 I will attempt to make con- 

 sistent use of it. 



A recent unfortunate intro- 

 duction of " ese " as a termination 

 for an enzyme which acts syn- 

 thetically only has been shown to 

 be unwarranted (Bayliss, 1913, 1) 

 and need not concern us further. 



FlG. 83. W. K.UHNE. 



(Photograph of the Tablet in the Institute 

 of Physiology, Heidelberg. ) 



We have seen that Berzelius himself placed the substances which we now call 

 enzymes in the class of catalysts. Apart from theoretical interest, it is of some 

 practical importance to know what kind of properties may be expected to be 

 shown by a substance supposed to be an enzyme. 



The only really essential property of a catalyst is that it changes the rate of 

 a reaction, including the starting of one which does not appear to proceed of 

 itself, and without entering as a constituent into the final chemical equilibrium. 

 There are certain other properties usually present, but not essential, although 

 they are sometimes of assistance in deciding the nature of particular cases. We 

 will now proceed to inquire how far enzymes satisfy the above conditions. 



It may be useful, first of all, to mention a few typical enzymes, remembering 



