90 Intraccllular Enzymes [Sept. 



increased six-fold, the increase being the same for both the pro- 

 tein and the erepsin. On the other band if ah'eady perfused sahne 

 is sent throiigh a second or a third time, the protein disruption is 

 diminished to one seventh, while that of the enzyme is increased 

 twenty fold. Different enzymes are apparently bound with differ- 

 ent degrees of firmness, for in two hours dilute alcohol will remove 

 55 per cent. of the total diastase and only 14 per cent. of the 

 trypsinogen from minced pancreas. 



The intracellular enzymes appear to be bound up in somewhat 

 the same way as the side chain receptors of Ehrlich. They are 

 bound with sufficient firmness to prevent their being cast off into 

 the blood stream in other than small quantities, some, such as mal- 

 tase, being liberated in larger amounts. The secretion enzymes, on 

 the other band, are liberated in large quantities whenever needed, 

 their linkage being more readily snapped by chemical or nervous 

 Stimulus. A few of the intracellular enzymes can be extracted with 

 comparative ease; glycerin apparently extracts endo-erepsin as 

 readily as exotrypsinogen and amylopsin. 



Enzymes may be regarded as similar to Ehrlich's " receptors 

 of the second order." Each enzyme has a group that may be 

 called its haptophoric group, which is supposed to attach itself to 

 a particle of Substrate and act upon it by its so-called zymophore 

 group. The intracellular enzymes are directly comparable to ag- 

 glutinating receptors while the secretion enzymes are comparable 

 to receptors which are over regenerated and cast off into the blood 

 stream, as when the blood of one animal is injected into that of 

 another. 



In some cases enzymes apparently act as " receptors of the 

 third Order," though there is no direct proof of this. They do 

 not bind themselves directly to particles of Substrate but only 

 through the Intervention of a third substance or amboceptor, as 

 for example in the conversion of fibrinogen into fibrin. Again it 

 has been shown that ptyalin, inactivated by heating to 53° C. can 

 be reactivated by adding blood, showing probable existence in ptya- 

 lin of a thermostable substance and a non-specific kinase present 

 in the blood and tissue extracts as well as in saliva. 



There is other evidence of the presence of haptophorous and 



