LIBEEATION OF ENERGY 129 



product. This suggests that the same cycle of reactions is 

 occurring in Esch. coli as previously demonstrated in yeast. 



If we assume that the initial steps in the breakdown are 

 those shown in Table XII, then the rest of the chain of 

 reactions has been proved. Using various methods for the 

 disruption of cells (see Chap. Ill), it has been possible to 

 obtain cell-free preparations of zymohexase (aldolase), 

 isomerase, glyceraldehyde-phosphate dehydrogenase, phos- 

 phoglyceromutase, enolase, lactic dehydrogenase, coenzyme I, 

 and adenosine-tri-phosphate from Esch. coli, Aerobacter 

 aerogenes, etc. There is little doubt then but that the main 

 glycolysis cycle, as set out in Table XII, can occur in these 

 bacteria. In general, the enzymes that have been isolated 

 from bacteria are essentially similar in properties to their 

 counterparts in other cells. 



Liberation of energy 



The formation of pyruvic acid from glucose via the cycle 

 described above, results in the liberation of energy which is 

 available to the organism for growth purposes. This energy 

 is made available by the building up and subsequent rupture 

 of the various phosphate bonds in the cycle. The energy 

 content of phosphate bonds differs with the nature of the bond. 

 Thus phosphate ester bonds of the type we get in hexose- 

 diphosphate ( — CHgOPOgHg) liberate comparatively little 

 energy when they are broken, but enol-phosphate bonds 

 ( — COPO3II2) of the type we find in phospho-enol-pyruvic 

 acid are energy-rich, their rupture releasing about 12,000 cals. 

 per gram-molecule compared with 3,000 cals, liberated by 

 the rupture of an ester-bond. Glucose is thus phosphorylated 

 at a low energy level to hexosediphosphate, and this is built 

 up by the cycle of reactions to give the energy-rich bond in 

 phospho-enol-pyruvic acid. Energy cannot, of course, be 

 created and phosphoglyceric acid and phospho-enol-pyruvic 

 acid have approximately the same energy content, but whereas 

 the energy of phosphoglyceric acid is distributed over the 



CHEM. A. B. 9 



