w. D. Mcelroy and j. w. Hastings 171 



were performed in an effort to determine the fate of the labile phos- 

 phate groups. 



Analysis of samples of the reaction mixture at various times after 

 addition of ATP for labile phosphate estabhshed the fact that prac- 

 tically all the labile phosphate groups were still present. Since 

 hexokinase catalyzes the transfer of the terminal phosphate of ATP 

 to glucose, it was possible to determine whether the labile phosphate 

 was still available for this reaction. As shown in Table III, the addi- 

 tion of hexokinase and glucose 5 minutes after ATP caused a rapid 

 decrease in the labile phosphate level. In addition to the evidence 

 cited earlier concerning the presence of myokinase, the results in Table 

 III clearly establish the fact that the enzyme was present, since the 

 phosphate groups of ADP were made available for the phosphoryla- 

 tion of glucose upon the addition of hexokinase, 



TABLE III 



Effect of Hexokinase on Labile Phosphate in Luminescent System 



(McElroy, 1951b) 



(Values in micrograms per milliliter) 



Fractionation of the luminescent reaction mixture after the addition 

 of ATP with barium acetate showed that over 90% of the labile phos- 

 phate was precipitated as the barium salt. This barium-precipitable 

 labile phosphate could also enter into the hexokinase reaction. The 

 results indicate that the ATP was still present in the reaction mixture, 

 even though the light intensity was rapidly decreasing. 



