112 



CARBON METABOLISM II 



1 r 



Dry weight 



16 



Time, days 



Figure 1. Amylase liberation by Aspergillus oryzae. Redrawn from Crewther and 

 Lennox (58), by permission of the Australian Journal of Biological Sciences. 



Amylase is, with some exceptions (64), found in the culture medium 

 as well as in the cells. The amount of enzyme is usually increased by 

 inclusion of starch in the growth medium (92, 210) and is affected by 

 the nitrogen source (210) and by small amounts of salts (69). Figure 

 1 illustrates the time course of appearance of extracellular amylase in 

 Aspergillus oryzae; it is to be noted that the peak of amylase activity 

 in the culture filtrate is reached only after the onset of autolysis. 



It has been reported (28) that the culture filtrate of Streptomyces 

 microflavus forms gentiobiose during the hydrolysis of starch. 



The Breakdown of Cellulose. Since many fungi utilize cellulose 

 as a carbon source (Chapter 3), it is to be expected that an enzyme or 

 enzymes are released from the cell and hydrolyze cellulose to soluble 

 sugars. Cellulose-hydrolyzing preparations free of living cells have 

 indubitably been made from several fungi (83, 191, 214), and dis- 

 tinguished from enzymes acting on lichenin and hemicelluloses (90). 

 However, two important limitations apply to most of the reported 

 work on cellulase: (1) native cellulose is relatively resistant to attack, 

 and most assays of "cellulase" have therefore utilized various types 

 of modified cellulose; (2) most data derive from studies with crude 

 cellulase preparations contaminated with other carbohydrases and 

 with interfering proteins (232). It is difficult, therefore, to assign more 

 than a descriptive value to much of the work so far reported. 



