72 Perspecfives m Microbiology 



down has special advantages to the cell because it makes 

 available a variety of carbon chains of differing lengths. 

 In fact, compounds containing one to seven carbon atoms 

 are formed from the hexose molecule by a most ingenious 

 system of group transfer reactions. The advantage of such 

 an assortment of compounds to a cell engaged in the syn- 

 thesis of a great number of more or less complex com- 

 pounds is obvious. For example, the pentose phosphate can 

 be used immediately for making ribonucleic acids and a 

 variety of ribose-containing coenzymes. Probably each of 

 the other compounds also serves as the starting point for 

 some synthetic process. 



Although much of the experimental work that has estab- 

 lished this oxidative mechanism was done ^^vith yeast, liver, 

 and plant enzymes, there is abundant evidence that some 

 bacteria including Escherichia coli (21) and Azotobacter 

 vinelandii (17) also utilize this mechanism of glucose oxida- 

 tion. 



A perhaps similar nonglycolytic mechanism, which has 

 long been suspected to exist but which has only recently 

 been demonstrated in a convincing manner, is found in the 

 fermentative bacterium Leuconostoc mesenteroides. Gayon 

 and Dubovag showed in 1894 that the fermentation of one 

 mole of glucose by Leuconostoc species yields one mole 

 each of lactate, ethanol, and carbon dioxide. The remark- 

 able feature of this fermentation, from the point of view of 

 the mechanism of sugar decomposition, is the constancy in 

 the yields of the three products. Other bacterial glucose 

 fermentations result in formation of the same compounds, 

 but the ratio of lactate to ethanol, for example, is highly 

 variable with pH and other environmental factors. With 

 Leuconostoc, half of the sugar is ahvays converted to lactate 

 and half to ethanol and carbon dioxide. This result is in- 

 consistent with the glycolytic mechanism, which requires 

 both halves of the sflucose molecule to follow a common 

 path between glyceraldehydephosphate and pyruvate. 



