468 DIGESTION 



sucrase, maltase and amylase; the stems, sucrase, amylase, inulase, and emul- 

 sin, while the roots contain amylase, inulase and emulsion (Robertson, et al., 

 1909). Germinating seeds are the richest of all plant organs in enzymes and 

 are generally used as the source of enzymes in experimental work. 



In some tissues the enzyme and corresponding substrate are both present 

 but only in adjoining cells. This is true, for example, in the seeds of the 

 bitter almond where the enzyme emulsin and its substrate amygdalin both 

 occur but not in the same cells. When bitter almond seeds are crushed the 

 enzyme and its substrate are brought into contact and hydrolysis of the 

 glycoside proceeds (Chap. XXII). More frequently the substrate and the 

 enzyme which catalyzes its hydrolysis are both found in the same cell. 

 Whether or not hydrolysis of the substrate will proceed is dependent upon 

 the conditions which prevail within the cells. It is almost invariably true 

 that plant tissues which are rich in a certain substrate will be relatively rich 

 in the corresponding enzyme, or at least its zymogen, and vice versa. 



Some plant enzymes, at least, maintain their potency for long periods of 

 time. Miehe (1923) has demonstrated that rye seeds which were at least 

 112 years old still contained amylase which would hydrolyze starch. 



The individual enzymes of most frequent occurrence in plants will now 

 be briefly discussed. The carbohydrases will first receive attention. 



Amylase (also called diastase^) is one of the enzymes of most wide- 

 spread occurrence in plants. It effects the hydrolysis of starch to maltose 

 through the intermediate stages of the dextrins (Chap. XXII). This enzyme 

 is sometimes considered to consist of a mixture of one or more amylases 

 and one or more dextrinases. Amylase is almost invariably present in the 

 green parts of plants, and is usually found in non-green organs or tissues 

 as wtW. This enzyme is also produced by many bacteria and fungi, as well 

 as by most animals. 



Commercial diastase is prepared from germinating barley seeds (malt) 

 in which the enzyme was first discovered. Takadiastase, another commercial 

 form of this enzyme, is prepared from colonies of a mold {Aspergillus oryzae) 

 which has been allowed to grow on a substrate of steamed wheat bran or rice. 



It is generally considered that there are two well-defined types of plant 

 amylase or diastase, the so-called "secretion diastase" and the so-called "trans- 

 location diastase." The former of these is secreted by specialized cells and 

 is only known to occur in the grains of corn, wheat, barley, and other mem- 

 bers of the grass family (Brown and Morris, 1890). "Translocation dias- 

 tase," on the other hand, is widely distributed in plant tissues and is especially 



^ This term is also sometimes applied to enzyme extracts which consist of a 

 mixture of amylase and maltase. 



