128 PHYSIOLOGY OF THE FUNGI 



ammonia which results from deamination. In general, the amino acids 

 appear to be poor sources of carbon. 



GLYCOSIDES 



The carbon sources to be discussed in this and the next two sections 

 differ from those previously considered in that they undergo hydrolysis. 

 The complex carbohydrates and carbohydrate-like compounds yield 

 simple sugars w^hen hydrolyzed. In some instances, other compounds 

 are also formed. In most instances, fungi utilize these compounds only 

 after hydrolysis. Therefore, utilization will be dependent upon the pro- 

 duction of the necessary hydrolytic enzymes. If a fungus is unable to 

 perform this preliminary "digestion," such complex carbohydrates will 

 be unavailable. 



Many of the compounds to be considered in this section are isomers. 

 The simple sugars exist mainly in the form of ring structures, rather than 

 the open-chain forms which were depicted in the previous sections of this 

 chapter. The chemical evidence may be reviewed in Pigman and 

 Goepp (1948) or other text dealing with the sugars. Glucose exists in 

 aqueous solution as an equilibrium mixture of a-D-glucose and /3-D-glu- 

 cose. These formulas contain a six-membered ring of w^hich one atom is 

 oxygen (pyranose). Some sugars, however, contain a five-membered 

 ring (furanose). 



The formulas for these two forms of glucose are given below: 



H OH HO H 



\ / \ / 



c , c- 



H— C— OH 

 HO— C— H 

 H— C— OH 

 H— C— O— 



H— C— OH 



I 

 HO— C— H 



I 

 H— C— OH 



I 

 H— C— O— 



CH2OH CH2OH 



a-D-Glucose /3-D-Glucose 



The simple glycosides are a widely distributed group of naturally 

 occurring compounds which contain a sugar moiety and an alcohol or 

 phenol moiety. The form glucoside was formerly used to designate com- 

 pounds of this type irrespective of the sugar moiety. Specific glycosides 

 are designated by adding the ending oside to the name of the sugar 

 involved; e.g., glucoside, mannoside, etc. 



Two glucosides are formed when glucose is treated with methanol 

 under appropriate conditions. The formulas are given below: 



