PRINCIPLES OF GENERAL PHYSIOLOGY 



with a true equilibrium in a reversible reaction (see Figs. 80 and 81, page 

 300 above). 



We see then that enzymes are, beyond doubt, typical catalysts in the 

 comparatively simple cases hitherto considered. Since, however, many of the 

 reactions taking place in the living organism under the influence of enzymes are 

 of a complex chemical nature, not as yet completely understood, it is not to be 

 wondered at that we meet with phenomena which seem, at first sight, to be 

 difficult to reconcile with the hypothesis of catalysis in reversible systems. We 

 shall presently meet with further evidence that, in cases of enzyme action where 

 we have all the factors under control, the reactions obey all the laws they would 

 be expected to do on the hypothesis mentioned. It appears to me that we 

 are hereby justified in holding that the more complex cases, such, for example, as 

 those where proteins are concerned, will be found to require no assumptions 

 contrary to the laws obeyed in the simpler cases. In these heterogeneous, colloidal 



-o-e 



10 \? 14 16 18 ^0 12 24- 



FIG. 84. RATE OF SYNTHESIS OF ULYCEROL-GLCCOSIDE WITH DIFFERENT CONCENTKA- 

 TIONS OF EMULSIN. The ratios are as 1 :4 : 12, the uppermost curve having the 

 lowest concentration. All arrive finally at the same position of equilibrium. 



(Bay lisa, 1913, 1, p. 246.) 



systems, the facts brought forward in the preceding chapters are sufficient to 

 indicate what innumerable possibilities of modification are present, in the way 

 of surface action, electric charge, and so on. It is the work of the future to 

 investigate the intervention of these factors in the course of the chemical reactions 

 brought about by the various individual enzymes. 



Certain incidental properties common to inorganic catalysts and enzymes serve 

 to strengthen our position. The fact that very minute quantities are active has 

 been mentioned already : how minute the really active substance is in the case of 

 enzymes we do not know, owing to the difficulty of preparing them in a chemically 

 pure state from the complex mixtures in which they are found. 



In the definition of enzymes, we sometimes find the qualifications introduced that they are 

 colloidal, specific catalysts destroyed by heat. It is true that the substances which we 

 separate as active enzymes are practically all in the colloidal state, but we are not absolutely 

 certain that this state is necessary to their activity in all cases. As to #pecifc nature, the 

 circumstance that a particular catalyst acts on a limited class of substrates is by no means 

 peculiar to those produced by living organisms ; some inorganic catalysts are very specific, as, 

 for example, tungstic acid is a powerful catalyst for the oxidation of hydriodic acid by 

 hydrogen peroxide, but not for its oxidation by persulphates or by bromic acid. On the other 

 hand, some enzymes are not particularly specific, emulsin acts on the whole series of 



