OCCURRENCE OF HYDROLYTIC PLANT ENZYMES 471 



in the seeds of both sweet and bitter almonds and various organs of other 

 members of the Rosaceae. Emulsin is also found in some fungi and inverte- 

 brates, but is not known to occur in any of the higher animals. 



The term esterases is applied to the general group of enzymes that 

 catalyze the hydrolytic splitting of esters into simpler compounds. The 

 most important sub-group of the esterases are the fat-hydrolyzing enzymes 

 or lipases. The term lipase is generally used in a collective sense in speaking 

 of the enzymes of this group, as it is by no means certain w^hether there is 

 only one lipase or a number of different lipases. The latter view is perhaps 

 more generally held. Lipase is known to catalyze both the digestion of 

 fats to fatty acids and glycerol as well as the synthesis of fats from these 

 two compounds. Lipase is present in greatest abundance in germinating seeds 

 containing relatively large quantities of fats, such as castor bean, soy bean, 

 coconut, flax, hemp, rape, and corn. Its presence can also be demonstrated 

 in the resting seeds of some, but not all, of these species. In those in which 

 it cannot be demonstrated in the seeds prior to germination it is believed to 

 be present in the form of a zymogen. This enzyme is also found in animals 

 and in some species of bacteria. 



As shown in Table 43 three different kinds of proteinases are recognized 

 (Grassmann, 1932). Of these the papainases are the most common in plants. 

 Papain is the best known of this group of enzymes. It occurs throughout 

 the tissues of the tropical papaw {Carica papaya) a species native to Central 

 and South American regions, but now cultivated in many other parts of the 

 world, including southern Florida. Natives of regions where this plant grows 

 have long known that its leaves have a digestive effect on meat. It is said 

 that simply wrapping meat in crushed papaw leaves will increase its tender- 

 ness. Commercial preparations of papain are prepared from the latex of this 

 species in which it is especially abundant. Incisions are made in the plant, 

 the milky exudate is collected, dried, and pulverized, and in this form be- 

 comes the "papain" of commerce. 



Brotneli?i is a papainase w^hich occurs in considerable quantities in the 

 pineapple (Ananas sativa) and other members of the Bromeliaceae. A crude 

 extract of bromelin can be obtained by squeezing out the juice of a fresh, 

 ripe pineapple. By suitable treatments purified and concentrated extracts 

 of this enzyme can be prepared. 



Reactions catah'zed by proteinases generally proceed at a much slower 

 rate than most other enzymatic reactions catalyzed by plant enzymes, at least 

 under laboratory conditions. An amylase extract which will hydrolyze a 

 fairly concentrated starch sol in a few minutes can be easily prepared but 

 hydrolysis of proteins by proteinases requires from several hours to several 



