THE EM BDEN-ME YERHOF PATHWAY 215 



and actinomycetes (60, 131, 237, 238, 257); the presence of nitrite in- 

 creases pyruvate formation by Fusarium spp. (220). Added thiamine 

 decreases pyruvate accumulation (273, 323), presumably by reason of 

 its function in diphosphothiamine, the coenzyme of pyruvic car- 

 boxylase. 



The formation of ethanol, acetaldehyde, and pyruvic acid is con- 

 sistent with the functioning of a pathway of the yeast type, as is the 

 appearance of other minor products (53, 109, 237, 255, 281), but does 

 not prove the occurrence of the pathway in any sense. 



The occurrence of lactic acid among fungi has been reviewed in the 

 preceding chapter. Among the phycomycetes, the only true fungi to 

 form large amounts of lactate from glucose, there appear to be two 

 different types of metabolic pattern. The lower phycomycetes so 

 far investigated anaerobically convert virtually all of the glucose con- 

 sumed to lactic acid (40, 41, 114, 145). This immediately suggests 

 comparison to the metabolism of muscle and of the homofermentative 

 bacteria, in both of which glucose is converted anaerobically to two 

 moles of lactic acid via the Embden-Meyerhof pathway. The com- 

 parison must, of course, be only tentative in the absence of further 

 data; the demonstration of a diphosphopyridine-linked lactic dehy- 

 drogenase would be of especial interest. 



Members of the genus Rhizopus constitute the second group of 

 lactate-forming fungi. Under anaerobiosis glucose is converted to 

 lactic acid in 50 per cent yield; Waksman and Foster (310) suggest the 

 over-all reaction: 



Glucose — » lactic acid + ethanol + C0 2 (4) 



The data of Table 1 show that R. oryzae ferments labeled glucose as 

 expected from the Embden-Meyerhof sequence, that is, the path of 

 glucose carbon is presumably, in outline: 



C3,4 



C2,5 



CI /Cl,6 



02 C3 4 L act i c a cid 



C3 -> C2,5 (5) 



C4 Cl,6 



G5 \ C2,5 + C3,4 



C6 Cl,6 



Glucose Pyruvic acid Ethanol CO2 



This implies that all products arise from a common pool of triose 

 phosphate, leaving open the problem of how the 1:1 ratio of lactic acid 

 to ethanol (Equation 4) is maintained. The conversion of pyruvate to 



