CHAPTER 4 

 ENZYMES AND ENZYME ACTION 



The fungi, in common with other hving organisms, possess tools or 

 reagents far more specific, more deHcate, and more powerful than those 

 available in the laboratory. The most complex natural substances such 

 as proteins, polysaccharides, and Hpoids are degraded into simpler com- 

 pounds which are soluble in water. Fungi also synthesize similar com- 

 plex compounds from relatively simple molecules. These transformations 

 are carried out under such mild conditions of temperature and pressure 

 and in such low concentrations of acid and alkali that it is certain the 

 means used are of a peculiar kind. For in the absence of these special 

 agents formed by the living organisms, these reactions do not take place 

 or do so at a very slow rate. These organic catalysts produced by living 

 organisms are called enzymes. The life processes of organisms are con- 

 trolled and directed by a complicated and interrelated series of enzymes 

 or enzyme systems (Dixon, 1949). 



Some enzymes formed by fungi are excreted and normally perform their 

 functions outside the cells that produce them. These are termed exo- 

 enzymes (extracellular enzymes), such as cellulase, amylase, and pectinase. 

 Exoenzymes perform the functions of digestion; i.e., the degradation of 

 complex food materials into low-molecular-weight compounds which are 

 able to enter the cell. After entering the cell, these metabolites are acted 

 upon by the enzymes within the cell. These enzymes are called endo- 

 enzymes (intracellular enzymes). 



Naturally enough, exoenzymes were recognized and studied first. In 

 the early literature, these exoenzymes were called unorganized ferments 

 because of their solubility. In contrast to these unorganized ferments it 

 was recognized that other ferments (enzymes) occurred in an insoluble 

 organized form. These were called organized ferments. Pasteur (1875) 

 still spoke of yeast as "ferment alcoohque ordinaire du vin." Thus, the 

 name organized ferment took on a dual meaning, that of a living organism 

 and the various chemical reactions caused by these organisms. In 1878 

 Kiihne suggested that the word enzyme be used to replace the terms 

 organized and unorganized ferments. Enzyme is derived from the Greek 

 phrase, en zyme, which means in yeast or leaven. For excellent sum- 

 maries of the historical development of the relation between fermentation 



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