ENZYMES AND THEIR ACTION 197 



pie. There is no known explanation for this type of activation of 

 the enzyme. 



The influence of activators, or inhibitors, in providing favorable 

 or unfavorable conditions for the action of an enzyme, should not 

 be confused with the relation to the enzyme itself of what are 

 known as " coenzymes " and " antienzymes," discussed in the fol- 

 lowing paragraph. 



COENZYMES AND ANTIENZYMES 



In the cases of many enzymes of animal tissues, it has been 

 found that they are absolutely inactive unless accompanied by 

 some other substance which is normally present in the gland, or 

 protoplasm, which secretes them. Thus, the bile salts are abso- 

 lutely necessary to the activity of trypsin, in its characteristic 

 protein-splitting action. Such substances are known as " coen- 

 zymes." They can usually be separated from their corresponding 

 enzymes by dialysis, the coenzyme passing through the parch- 

 ment membrane. Such coenzymes are not killed by boiling 

 the dialyzate, and the activity of the enzyme is restored by adding 

 the boiled dialyzate to the liquid which remains within the 

 dialyzer. 



The best known example of a coenzyme in plant tissues is in 

 connection with the activity of the zymase of yeast cells. If 

 yeast juice be filtered through a gelatin- filter, the colloidal enzymes 

 which are left behind are entirely inactive in producing fermenta- 

 tion, but may be restored to activity again by mixing with the 

 filtrate. An examination of this filtrate, which contains the coen- 

 zyme for zymase, shows that it contains soluble phosphates and 

 some other substance whose exact nature has not yet been deter- 

 mined, both of which are necessary to the activity of the zymase. 

 The phosphates seem to enter into some definite chemical combina- 

 tion with the substrate sugars, while the other coenzyme seems to 

 be necessary in order to make possible the final breaking down of 

 the sugar-phosphate complex by the zymase. This phenomenon 

 of coenzyme relationship is not very frequently observed in plant 

 enzyme studies, probably because the coenzyme (if there be such, 

 in the case which is under observation) usually accompanies the 

 enzyme itself through the various processes of extraction and 

 purification of the material for study. However, care must be 



