THE ROLE OF GREEN PLANTS 26:5 



Enzymes and Their Work 



The changes just described which take place in food making as well 

 as in food storage, all belong to a series of oxidative and reducing 

 changes that are presided over and brought about by enzyme action, 

 another indication of the importance of these omnipresent substances. 



We have already spoken of enzymes and their work, but reference 

 to them again may not be amiss at this point. They are found 

 practically everyw^here in the living cells of plants and animals, being 

 much more numerous than was at first believed. Although their 

 nature is not fully known, we do know that they are colloidal sub- 

 stances, because they will pass through porcelain filter, but not 

 through membranes. We also know that some of them are doubtless 

 proteins, and that they are sensitive to light and ultraviolet rays as 

 well as to heat, acid, alkali, and substances which are toxic to proto- 

 plasm. They are powerful catalyzers, as is shown by the fact that a 

 single gram of the enzyme invertase, for example, will quickly hy- 

 drolyze one million times its weight of sugar. Enzymes are found in 

 all living cells and are specific in action, that is, one enzyme will only 

 do a certain type of w^ork. In general, they may be divided into a 

 number of groups, depending upon their function, such as the hy- 

 drolases, that act in the digestive processes of plants and animals by 

 hydrolyzing materials ; the oxidases, which enable cell respiration to 

 take place ; the fermentases, as, for example, remiin, that is used in 

 cheese making, and the coagulascs, to which pedasc belongs that is 

 used commercially in substances sold for use in jelly making; and 

 finally, the carboxylases, which cause organic acids to split into carbon 

 dioxide and other simpler substances. 



Specific examples of these various plant enzymes include the en- 

 zyme, diastase, that causes the digestion of starch. Another enzyme, 

 maltase, aids in the digestion of maltose to glucose, a still simpler 

 sugar. A similar action takes place by means of the enzyme, ptyalin, 

 in our own salivary digestion. Bacteria carry on a slightly different 

 type of digestion in which cellulose or wood fiber is broken down and 

 used as food. Here another enzyme, cellulase, causes this digestive 

 change. Still another enzyme, called lipase, is instrumental in the 

 digestion of fats. In fruits and seeds rich in fat, such as the avocado, 

 Brazil nut, walnut, almond, or pecan, the fats are broken down into 

 fatty acids and glycerine just as in animals where lipase is formed by 

 the pancreas. 



H. w. H. — 18 



