CARBON SOURCES 129 



H OCH3 H3CO H 



C , C- 



H— C— OH 



I 

 HO— C— H 



I 

 H— C— OH 



I 

 H— C— O— 



H— C— OH 

 HO— C— H 



H— C— OH 



I 

 H— C— O— 



CH,OH CH2OH 



a-Methyl-D-glucoside /3-Methyl-D-glucoside 



These formulas correspond to the alpha and beta isomers of glucose. 

 The proof that a-methylglucoside and a-glucose have the same structure 

 was furnished by Armstrong (1903), who followed the enzymatic 

 hydi'olyses of these glucosides polarimetrically. 



Our interest in the glycosides is not in the chemical structure per se, 

 but in the fact that utilization of these and other compounds having the 

 same type of glycoside linkage is dependent upon configuration. Differ- 

 ent enzymes are required for the hydrolysis of the a- and /3-glycoside 

 linkages. Some fungi possess both types of hydrolytic enzymes, others 

 but one, and some fungi appear to lack both. Thus, certain yeasts 

 ferment a-methylglucoside but not /3-methylglucoside. These yeasts 

 have an enzyme or enzymes which catalyze the hydrolysis of the a-gly- 

 coside linkage but not the /3-glycoside linkage (lactose-fermenting yeasts 

 are able to hydrolyze ;S-glycosides). 



The use of the methylglucosides is not always a safe guide in pre- 

 dicting which complex sugars will be utilized by fungi. Aspergillus niger 

 utilizes /3-methylglucoside rapidly and completely, while a-methyl- 

 glucoside is poorly utilized (Dox and Neidig, 1912). Attempts to adapt 

 A. niger to utilize a-methylglucoside as a sole source of carbon were 

 without much success, although the fungus apparently utilized this 

 compound in the presence of sucrose (Dox and Roark, 1920). A. niger 

 utilizes lactose poorly. Tamiya (1932) found A. oryzae made only a 

 trace of growth on a-methylglucoside. /3-Methylglucoside was not 

 tested. This fungus grows well on maltose. These results are, perhaps, 

 not unexpected in view of the specificity of enzymes. The utilization of 

 the naturally occurring simple glycosides by fungi has been investigated 

 but slightly. 



OLIGOSACCHARIDES 



These sugars are derived from two, three, or four hexose sugars by the 

 elimination of water. On hydrolysis, the individual sugars are regener- 

 ated. Five factors which determine the structure of the oligosaccharides 

 are (1) the component sugars; (2) the component sugar which functions 



