OLIGOSACCHARIDES 105 



molecule, but there is no evidence directly on this point in the fungi 

 and actinomycetes. 



Free sugars appear in the mycelium (130, 227) and in the culture 

 medium (84, 85), but their significance is not known. 



The phosphate esters of the monosaccharides are hydrolyzed by 

 phosphatases (phosphomonoesterases). The phosphatases active on 

 glycerophosphoric acid may be presumed to act also on hexose phos- 

 phates. No direct study of these reactions in fungi has been made, 

 but there is no doubt that at least the common saprophytic fungi and 

 actinomycetes can hydrolyze hexose and pentose phosphates; commer- 

 cial enzyme preparations made from fungi contain acid phosphatases 

 (179) and have been used in many laboratories for the dephosphoryla- 

 tion of sugar phosphates. Phosphatases are considered in more detail 

 in Chapter 9. 



2. THE METABOLISM OF OLIGOSACCHARIDES 



The literature on the enzymatic breakdown of disaccharides and 

 trisaccharides by fungi is extensive but, as in so much of fungus physi- 

 ology, relatively few types have been studied. Most of our informa- 

 tion comes from work on the Fungi Imperfecti, the wood-destroying 

 basidiomycetes, and the Saprolegniaceae. Many other groups of fungi 

 have not been investigated and must, therefore, be excluded from any 

 generalization. 



The most significant recent advance in our approach to the break- 

 down of oligosaccharides is the concept of transglycosidation. Until 

 the formulation of this concept the breakdown of sucrose, for example, 

 was visualized as a simple hydrolysis: 



G12H22O11 + H 2 -+ G 6 H 12 6 + C 6 H 12 6 (1) 



Sucrose Glucose Fructose 



Since sucrose is made up of glucose and fructose units linked by a 

 glycosidic bond, this hydrolytic reaction may be schematized: 



Fr— Gl -> Fr + Gl (2) 



It now appears that at least some and possibly all of the so-called 

 hydrolytic enzymes are in fact group transferases, capable of transfer- 

 ring a sugar residue to any suitable acceptor. The acceptor may be 

 water, in which case Equation 2 describes the reaction, but other sugars 

 or alcohols can also serve as acceptors. In a particular case, the action 

 of yeast invertase, the fructose residue of sucrose is believed to be 

 transferred as follows (72): 



