212 RESPIRATION 



4. OXIDATIVE ASSIMILATION 



Oxidation of carbon compounds by many organisms is not accom- 

 panied by the oxygen uptake theoretically necessary to account for the 

 known disappearance of substrate. This has been explained as the 

 result of the assimilation of part of the utilized carbon into reserves, 

 presumably carbohydrate in nature, of the cell (59). 



Oxidative assimilation occurs in yeast (234, 322), actinomycetes 

 (254), and fungi (70, 80, 253). Its extent may be rather high; for 

 Penicillium chrysogenum (272), the data fit the equation: 



C 6 H 12 6 + 2 -> 5(CH 2 0) + C0 2 +H 2 (3) 



Thus, in this organism about 83 per cent of the glucose disappearing 

 is assimilated. 



Fermentative, i.e., anaerobic, assimilation is known in yeast and 

 bacteria (297). In what is presumably the same process, Aspergillus 

 niger forms intracellular mannitol and carbohydrate anaerobically 

 (255). Fermentative accumulation may account for the finding (154, 

 247) that A. niger forms less ethanol from glucose than the theoretical 

 amount expected from a fermentation of the yeast type. 



5. THE EMBDEN-MEYERHOF PATHWAY 



The anaerobic breakdown of glucose by yeast is diagrammed in part 

 in Figure 4. This series of reactions is of very general, although 

 probably not universal, occurrence in microorganisms (79, 118). In 

 muscle the reactions, termed glycolysis, are similar, except that pyruvic 

 acid is reduced to lactic acid in the final step and that the starting 

 material is glycogen. 



Since the filamentous fungi require oxygen for growth (Chapter 1), 

 there has been a tendency to discount the possible importance of the 

 Embden-Meyerhof pathway. First, it should be realized that the 

 products of glucose metabolism by other routes may feed into the 

 pathway; thus the phosphogluconate oxidation pathway, as discussed 

 later, forms triose phosphate. Second, the Embden-Meyerhof pathway 

 is not restricted to anaerobic conditions; it is entirely possible for a 

 portion of it to function simultaneously with aerobic processes or to 

 be coupled to terminal aerobic reactions. Finally, some fungi seem 

 to be able to ferment sugar anaerobically even though they require 

 oxygen for growth. 



Although in the bacteria there are routes of ethanol formation other 



