OTHERGLYCOSIDES 109 



reserve carbohydrate, formed early in metabolism and used up later 

 (43); under some conditions reutilization may not occur during the 

 life of the fungus (164). An adequate picture of the course of trehalose 

 synthesis and breakdown is not yet available. In yeast, trehalose is 

 synthesized as its phosphate from glucose and a glucose phosphate, 

 with uridine diphosphate glucose as coenzyme (68, 125); whether the 

 same mechanism is operative in the filamentous fungi remains to be 

 seen. 



Melibiose, an a-galactosido-glucose occurring naturally as a con- 

 stituent of raffinose, is split by an a-galactosidase (melibiase) known in 

 yeast and higher plants and reported from Aspergillus spp. (100, 230). 



Trisaccharides and Tetrasaccharides. Raffinose, composed of galac- 

 tose, glucose, and fructose, is split by enzymes from most fungi which 

 have been tested. This is to be expected, in view of the fact that 

 sucrase splits raffinose to melibiose and fructose. The complete 

 hydrolysis of raffinose requires both sucrose and melibiase; melibiase 

 alone yields sucrase and galactose. In all likelihood, hydrolysis of 

 raffinose by unspecified fungal enzymes should usually be attributed 

 to sucrase (2, 15). 



Melezitose is hydrolyzed, at least partially, by several fungi (15, 

 122). Detailed studies of the reaction are lacking; complete hydrolysis 

 requires an enzyme able to attack the disaccharide turanose. 



Gentianose is completely hydrolyzed to glucose and fructose by an 

 enzyme preparation from Aspergillus niger (40, 41); the effective 

 preparation has been shown (42) to contain a /3-glucosidase acting on 

 the gentiobiose moiety of gentianose. 



Stachyose, a tetrasaccharide composed of galactose, glucose and 

 fructose in the ratio 2:1:1, is split by enzymes from Penicillium 

 spinulosum and Aspergillus spp. completely to its constituent sugars 

 (15, 228). Presumably sucrase and an a-galactosidase are required. 



3. THE METABOLISM OF OTHER GLYCOSIDES 



The oligosaccharides, just considered, are one class of glycoside, in 

 which the glycosidic bond connects two monosaccharide residues. The 

 same bond can be formed between a sugar and certain other molecules; 

 the non-carbohydrate moiety of the resulting compound is then 

 termed an aglycon. Information on the metabolism of glycosides of 

 this type by fungi is restricted to a few compounds, in all of which 

 glucose or mannose is the sugar involved. 



The /3-glucosides have received more attention than any others in 



