Mechanism of Glycogen Synthesis in Muscle 191 



an analogous experiment is presented using glucose-6-phosphate as 

 the glucose donor for incorporation. Although here some incorpora- 

 tion is maintained even with added kinase, its addition obviously 

 depresses the incorporation. At the same time, as seen on the right- 

 hand part of Fig. 5, it appears that with kinase added, glycogen 



Control 

 Pho3phopylase 

 kinase added 



Time in minutes 



Fig. 4. Effect of phosphorylase kinase on the incorporation 

 of glucose into glycogen. The experiments were carried 

 out in Warburg flasks as described by Robbins, Traut 

 and Lipmann (1959). The homogenates were supplemented 

 with kochsaft (0-2 ml./ml.) and with crystalline phos- 

 phorylase b (Fischer and Krebs, 1958). Phosphorylase 

 kinase was prepared according to Krebs and Fischer (1956). 

 Incorporation was measured as described previously 

 (Robbins, Traut and Lipmann, 1959) and phosphorylase 

 was assayed according to Cori and co-workers (1955). 



disappearance was accelerated. It may be noted that the induction 

 period for incorporation with free glucose is absent with glucose 

 phosphate. Apparently, conversion of glucose phosphate is more 

 direct (cf. below). 



The results of this experiment forced us to consider the possibility 

 that phosphorylase a may not be concerned physiologically with 



