124 PROVISION OF energy: fermentation 



A further consequence of obtaining energy by fermentation 

 is the accumulation of large quantities of waste products 

 which may be toxic to the organism in high concentration. 

 Consequently this form of metabolism is necessarily restricted 

 to small organisms living in a liquid medium, in which the 

 waste products are quickly removed by diffusion from the 

 immediate environment. 



The anaerobic breakdown of glucose has been studied in 

 considerable detail of recent years, and great advances have 

 been made in our knowledge of the processes that take place 

 during this breakdown ("glycolysis") in muscle and yeast 

 cells. In the case of these cells it is comparatively easy to 

 make cell-free extracts of the cells and, from these, to make 

 preparations of the various enzymes present. In this way it 

 has been possible to disentangle the various steps in the 

 series of reactions and to isolate the enzymes catalysing these 

 steps. Our knowledge of bacterial glycolysis has lagged 

 behind that for yeast and muscle cells, as it is only of recent 

 years that efficient methods have been discovered whereby 

 bacterial cells can be disrupted and their enzymes liberated 

 in an active state. Consequently there are still gaps in our 

 knowledge of bacterial fermentation processes, and much 

 of the work has been concerned so far with investigating 

 whether the stages of breakdown of glucose by bacteria are 

 the same as those occurring in yeast. As far as the processes 

 concerned in the formation of pyruvic acid are concerned, 

 the answer appears to be that these processes are essentially 

 the same in bacteria as in yeasts and in various other tissues 

 that have been investigated. 



BREAKDOWN OF GLUCOSE BY YEAST 



Table XII outlines the steps and enzymes involved in the 

 breakdown of glucose to pyruvic acid by yeast cells. The 

 first step consists of a phosphorylation of glucose to glucose- 

 6-phosphate by the enzyme hexokinase, which catalyses the 

 transfer of the phosphate group from adenosine-tri-phosphate 



