ENZYMES AND THEIR ACTION 191 



The above list includes only the more common and best-known 

 plant enzymes. It seems reasonable to suppose that for every 

 individual type of organic compound which may occur in general 

 plant groups, or even in single species, there is a corresponding 

 enzyme available to affect its physiological alterations. Indeed, 

 new preparations of active enzymes from special types of plants 

 and new evidences of the existence of enzymes in various plant 

 organisms are continuously being reported. 



A few of the most common specific representatives of individual 

 groups of enzymes may be briefly described, as follows: 



Amylase (or diastase, as it was first named and is still com- 

 monly called) is probably the most widely distributed enzyme of 

 plants. It is found in practically all bacteria and fungi; in prac- 

 tically all seeds (it has been found in active form in seeds which 

 were known to be over fifty years old); in all roots and tubers; 

 and in practically all leaves, where it is located in the stroma of the 

 chloroplasts. 



It appears to exist in two modifications, known, respectively, 

 as (a) translocation diastase and (6) diastase of secretion. The 

 first form is found in the cells of ungerminated seeds, in leaves, 

 shoots, etc. It remains in the cells where reserve starch is stored 

 and aids in the transformation of starch into soluble materials for 

 translocation from cell to cell. It is active at a lower temperature 

 than the second form, its optimum temperature being 45 to 50. 

 The second form is secreted by the scutellum, and perhaps by the 

 aleurone cells, of germinating seeds, being produced by special 

 glandular tissue. It aids in the hydrolysis of the starch for the 

 use of the growing embryo. Its optimum temperature is 50 to 55. 



The activity of amylase is accelerated by the presence of 

 small quantities of neutral salts, especially by sodium chloride and 

 disodium phosphate. It acts best in neutral solutions, its activity 

 being inhibited, although the enzyme itself is not destroyed, by the 

 presence of more than minute traces of free mineral acid or alkali. 



Sucrase (or invertase) is present in almost all species of yeasts, 

 where it serves to convert unfermentable sucrose into glucose and 

 fructose, which are readily fermentable. Invertase is also present 

 in moulds and other microorganisms; and in the buds, leaves, 

 flowers, and rootlets of those higher order plants which store their 

 carbohydrate reserves in the form of sucrose. It appears that 

 sucrose, while easily soluble, is not readily translocated, or utilized, 



