Short Communication: 



RECENT OBSERVATIONS ON THE MECHANISM 

 OF GLYCOGEN SYNTHESIS IN MUSCLE 



Phillips W. Robbins and Fritz Lipmann 



Rockefeller Institute for Medical Research, New York 



These experiments (Robbins, Traut and Lipmann, 1959) were 

 started as an attempt to go back to the type of preparation which 

 Krebs had used and where he found the maintenance effect of insuHn 

 on respiration, namely the pigeon breast muscle (Krebs and Eggles- 

 ton, 1938). We wanted, however, to assay for glycogen synthesis 

 and to look for an insulin effect on this reaction. We could not 

 obtain any set-up that synthesized glycogen in a controllable manner 

 with the originally used, coarsely cut muscle obtained with an 

 instrument rather similar to the Latapie cutter. However, after 

 some trial and error, a system was found using the conventional 

 homogenization technique which appeared useful for our purpose. 

 Although generally in the course of the experiment glycogen was 

 partially degraded, the synthetic activity could be followed by way 

 of radioactive glucose or glucose-6-phosphate incorporation into 

 glycogen. 



To get good incorporation, this system had to be supplied with 

 muscle kochsaft which could be replaced by coenzyme A, while 

 addition of pyridine nucleotides and adenosine triphosphate (ATP) 

 had no effect. The effect of CoA and kochsaft appears, however, to 

 be indirect since, as shown in Fig. 1, CoA addition maintained 

 respiration on which the glycogen synthesis depended. Oxidative 

 phosphorylation, which was the ultimate energy donor in this 

 system, could not be replaced by ATP or an energy-rich phosphate 

 feeder system. Perhaps the speed with which energy-rich phosphate 

 has to be fed could only be obtained by the mitochondrial system. 

 In any case, addition of dinitrophenol abolished incorporation. A 

 further activator appeared to be aspartate, which maintains the 

 level of adenosine phosphates ; in its absence, partial degradation to 

 inosinic acid was observed in the paper electropherogram. 



Fig. 2 gives a more detailed view of the CoA effect. The reason for 

 inhibition by higher CoA concentrations is not understood. It 

 should be added that the mere addition of sulphydryl carriers such 

 as glutathione or cysteine had no effect. The general metabolic 



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