110 CARBON METABOLISM II 



this general category. The enzyme /^-glucosidase (formerly termed 

 emulsin) occurs in almost all of the fungi and actinomycetes which 

 have been examined for it (31, 38, 39, 101, 147, 201, 229), although it 

 is not always found in the medium (191) and may not be so nearly 

 universal as, for example, maltase or amylase. Fusarium oxysporum 

 var. lycopersici forms detectable amounts of the enzyme within the 

 living infected plant (60). 



Although it is common practice to speak of a single /3-glucosidase 

 hydrolyzing all /3-glucosides — including the /3-linked disaccharides 

 cellobiose and gentiobiose — it seems more likely that a group of related 

 enzymes is involved (238) or that at least there are distinct com- 

 ponents of the enzyme (111, 112). The /3-glucosidases of Aspergillus 

 niger and A. oryzae, for example, act at different rates on different 

 synthetic /3-glucosides (151). The enzyme of A. niger has been purified 

 about 10,000-fold (160, 161). 



During the action of /?-glucosidase on synthetic /3-glucosides, the 

 glucose residue can be transferred to alcohols, indicating trans- 

 glucosidase activity similar to that with cellobiose as substrate (Table 



1). 



Alpha-glucosides, in principle at least, should be attacked by maltase, 



an a-glucosidase. However, maltases from different sources have differ- 

 ent behavior toward, e.g., methyl-a-glucoside, and the maltase of fungi 

 seems to be of minimum activity toward this substrate (89). A crude 

 preparation from Aspergillus niger hydrolyzes methyl-a-glucoside 

 slowly (65), and in some fungi there is an a-glucosidase distinct from 

 maltose (15), but the problem has been too little studied for any 

 definite conclusion to emerge. Aspergillus niger cultivated with 

 methyl-a-galactoside forms the corresponding a-galactosidase (182). 



An enzyme of Streptomyces griseus converts mannosidostreptomycin 

 to streptomycin (175). The enzyme has been found to split synthetic 

 methyl-a-mannoside (99) and may therefore be termed an a-manno- 

 sidase. The same action, with methyl-a-mannoside as substrate, is 

 known in Aspergillus niger (98). 



4. THE METABOLISM OF POLYSACCHARIDES 



The Breakdown of Starch and Glycogen. These two related polysac- 

 charides are hydrolyzed by amylases (diastases), of which there are in 

 nature two general types (154): 



1. Alpha-amylase (endoamylase, dextrinizing amylase, liquefying 

 amylase), found in animals and microorganisms. Attack on starch, at 



