ENZYMES 203 



they react with each other. The glucose molecules, for example, 

 are adsorbed so tightly by the molecules of maltase that two of 

 them unite to form maltose. This attraction may be of an electrical 

 nature or be due to some as yet unknown cause. 



Those who believe in a chemical combination theory hold that 

 the enzyme unites in some way with the reacting substances and 

 thus brings them together. When its work is done it withdraws 

 and then unites two others. The former (adsorption) theory may 

 be compared in its action with that of the village matchmaker 

 who brings the two parties together in her parlor and thus in- 

 creases the chances of their union, while the action demanded by 

 the latter theory is more comparable to that of the parson who 

 takes the hand of each and places it in that of the other, after 

 which he withdraws and goes on to the next couple. 



The nature of this chemical combination is not well understood. 

 Is it a sort of colloidal reaction or is it a chemical one in the ordinary 

 sense where molecules and atoms enter into new combinations? 

 The effect of heat upon the reacting substances; the appearance 

 of the materials under the ultramicroscope ; the fact that if an 

 enzyme and its substrate, each of which will pass through a given 

 filter, are mixed, the reacting mixture will not pass through the 

 filter; and the general colloidal nature of the enzymes, etc., all 

 point to a colloidal combination (e. g., adsorption), and the weight 

 of the evidence is in favor of this viewpoint; but the specific na- 

 ture of the enzymes might be considered as a strong argument in 

 favor of some kind of molecular combination. 



Willstatter's conception of enzymes is a sort of compromise be- 

 tween these two views. He thinks that the enzyme consists of a 

 colloidal complex or carrier, to which is attached the specific 

 catalytic group. This latter group possesses particular affinities 

 for definite molecular groupings of the substrate and explains the 

 chemical properties of the enzyme^ and its specificity. Thus, if we 

 assume that melezitose (Chap. XII) is glucose-levulose-glucose, 

 while rafnnose is galactose-glucose-levulose, an explanation is at 

 hand as to why Aspergillus invertase can hydrolyze melezitose but 

 not raffinose, while yeast invertase acts vice versa. In the first 

 case, the invertase attaches at the glucose molecule and in the sec- 

 ond case on the levulose. The colloidal carrier explains the colloidal 

 properties of the enzyme; when the properties of this aggregate are 

 destroyed (e. g., by heat or salts), the activity of the enzyme is 



