CATALYSIS AND ENZYMES 327 



have a powerful chemical substance which induces the disintegration of the snails, 

 representing the substrate, which are adsorbed on its surface. 



The exponential ratio of the concentration of the enzyme to its activity receives a satis- 

 factory explanation on this adsorption theory, as will be plain from the above illustration. 



On the other hand, it seems that we must either attribute some special 

 properties to the enzyme surface itself, which may be of the nature of configura- 

 tion, chemical or physical, or else we must suppose the formation of an inter- 

 mediate chemical compound between enzyme and substrate, to be afterwards 

 broken up into enzyme and products. The case of the relation between the a- 

 and /3-glucosides to maltase and emulsin will serve to show what is meant here. 

 The a-glucosides are scarcely acted on at all by emulsin, perhaps not at all, but 

 rapidly by maltase, and vice versa with regard to the /3-glucosides. Now it does 

 not seem possible that any ordinary surface could distinguish to such a degree 

 between the properties of two substances so nearly alike as the a- and /3-glucosides 

 of methyl are. At the same time, apart from their optical isomerism, they 

 have certain other differences, solubility for example. As was remarked before, 

 until we know more as to the possibilities of adsorption, it would be rash to be 

 dogmatic on the question. 



As to the configuration of the surface, it is quite conceivable that a particular pattern, so 

 to speak, may allow closer approximation of reacting molecules than another pattern does. 

 As a very rough illustration, a surface beset with projecting spikes would not allow so close 

 an approximation of a flat surface as would another flat surface. We must be careful, however, 

 not to be misled by too statical a conception of the phenomena. Moreover, there may be 

 true chemical combination with the actual chemical substance of the surface of a colloidal 

 aggregate, without the phenomena losing their characteristic adsorption nature. See also 

 Bayer and W. W. Starling (1915). 



ZYMOGENS 



When enzymes arise in the course of the growth of cells, it is plain that 

 they must pass through preliminary stages and it seems that what are called 

 "zymogens" constitute a stage of this kind. Sometimes we find the enzymes 

 secreted to the exterior in the inactive form ; the trypsinogen of the pancreatic 

 juice is such a case ; it requires the action of another enzyme, enterokinase, to 

 convert into active trypsin. Details of the phenomenon may be found in my 

 monograph (1913, 2, p. 132) and to some extent in the following chapter of this 

 book. 



We must note the difference between a zymogen and an enzyme which is 

 inactive on account of the want of its co-enzyme. The conversion of a zymogen 

 into an enzyme cannot be reversed by any process at present known to us, whereas 

 the co-enzyme can be added or removed at will. 



PRODUCTION OF ENZYMES 



There appears to be some evidence that enzymes may make their appearance 

 in response to the presence of an appropriate stimulus, or rather substrate. 

 Thus Duclaux (1899) stated that Penicillium glaucum, grown on different media, 

 produced enzymes which hydrolysed these media, enzymes which were absent 

 in other cases. 



A significant point with regard to the nature of enzymes is to be found 

 in their occurrence in situations where they have never had the opportunity, 

 in the course of evolution, of meeting with their special substrates, lactase in 

 the almond, for example. If this lactase is a selective enzyme acting only on 

 lactose it must have been produced, accidentally, as it were, as a by-product of 

 metabolism. Otherwise it must be regarded merely as an incidental property 

 of emulsin. 



The appearance of enzymes in the blood in response to injection of proteins or carbohydrates, 

 Abderhalden's "protective enzymes," requires further investigation. They are not specific, 

 that is, a particular sugar may set free the enzyme which hydrolyses it or another in addit on. 

 They are probably set free from some situation in the organism. The production of an enzyme, 

 not found somewhere in the organism, has not been shown to occur. 



