ENZYMES AND THEIR ACTION 187 



OCCURRENCE AND PREPARATION FOR STUDY 



Enzymes are present in all living matter. In animal tissues, 

 they occur in the largest amounts in those glands or organs where 

 active vital processes take place, as in the brain, the digestive 

 tract, blood, etc. In plants, they may be found in all living cells, 

 and are especially abundant in the seeds, where they serve to render 

 soluble and available to the young plant the stored food materials. 

 The enzymes of moulds, and other parasitic plants, are usually 

 extracellular in type, being secreted for the purpose of making the 

 material of the host plant available to the parasite. Extracellular 

 enzymes are also developed in seeds during germination, in order 

 that the stored food material of the endosperm may be rendered 

 soluble and translocated into the tissues of the growing seedling. 

 But most other plant enzymes are intracellular in type. Hence, 

 in all preparations of plant enzymes for study, or for commercial 

 use, the first step in the process is, necessarily, a thorough ruptur- 

 ing of the cell-walls of the plant material. 



The rupturing of the cells may be accomplished in a variety of 

 ways, as follows: (1) mechanical disintegration, as by grinding in a 

 mortar with sharp sand; (2) freezing the material, by treatment 

 with liquid air, then grinding; (3) killing the cells by drying, by 

 treatment with alcohol or acetone, then grinding the mass in a 

 paint mill with toluene; (4) killing the cells by chemicals (sulfuric 

 acid, 0.5 to 1.0 per cent, or other suitable agents) followed by 

 extraction with water; (5) autolysis, or self -digestion, in which the 

 cells are mixed with toluene or some other antiseptic which kills 

 the cells without injuring the enzymes, then the material is minced 

 or ground up and suspended in water containing the antiseptic, 

 until the enzymes dissolve the cell-walls and so escape into the 

 liquid this process being especially adapted to the preparation 

 of active extracts from yeasts, which contain the necessary cell- 

 wall dissolving enzymes to facilitate autolysis. 



Enzymes may be separated out of the aqueous extract obtained 

 from cells ruptured by any of the above methods, by precipitation 

 with alcohol, acetone, or ether, in which they are insoluble; but 

 if this is done, the precipitate must be at once filtered off and rapidly 

 washed and dried, as prolonged contact with these precipitating 

 agents greatly diminishes the activity of most enzymes.' Or, they 

 may be adsorbed out of solution on gelatinous, or colloidal, mate- 



