418 



BIOLOGICAL ENERGETICS 



available energy than the ATP alone could provide, since considerably- 

 larger amounts of CrP are present (Table 16-2) . In view of its metabolic 

 role, CrP has been called a phosphagen. Another phosphagen, arginine 

 phosphate, takes the place of CrP in the muscles of most invertebrates. 



Table 16-2 

 Relation of muscular activity to concentration of various substances in muscle 



* Values estimated from probable ATP-ADP-inorganic P ratios as calculated from 

 energy relations of aerobic and anaerobic metabolism (see M. J. Johnson, Chap. XII, 

 in Respiratory Enziimes, by Lardy : Burgess Publishing Company, Minneapolis, 1949). 



t Millimoles per kilogram, fresh weight. 



Still another phosphagen of unknown composition has been detected 

 in certain lower organisms. The amounts of phosphagens in various 

 tissues are shown in Table 16-2. By far the largest concentrations are 

 present in those muscles which are capable of the greatest work output 

 (striated muscle) . 



Generation of high energy phosphate bonds 



Glycolysis. The reactions of glycolysis, which result in the formation 

 of high energy bonds, are now known in detail. They have been presented 

 in Chap. 13 (Figs. 13-1 and 13-3, reactions 9 and 12) . In all, four '--'P 

 bonds are so generated for each hexose unit, that is, four molecules of 

 ADP are converted to ATP. However, two molecules of ATP are used 

 up along the way (reactions I and 4) so that the "net yield" to the 

 organism is two moles of ATP per mole of glucose metabolized to lactic 

 acid. Since each mole of ATP gives up 11,500 cal. when used for work 

 {i.e., hydrolyzed to ADP), this figure represents an energy yield from 

 glycolysis of 23,000 cal. per mole of glucose. The free energy change 



