VOL. 12 (1953) BIOCHIMICA ET BIOPHYSICA ACTA 235 



ENZYMIC CONVERSION OF PHOSPHORYLASE a 

 TO PHOSPHORYLASE b 



by 



PATRICIA J. KELLER* and GERTY T. CORI 



Department of Biological Chemistry, Washington University School of Medicine, 



St. Louis, Missouri (U.S.A.) 



Two forms of rabbit muscle phosphorylase were described by Cori and Green in 

 1943 : phosphorylase a which exhibits 60 to 70% of maximal activity without the addi- 

 tion of adenylic acid (adenosine-5'-phosphate), and phosphorylase b which has no or 

 minimal activity unless adenylic acid is added to the reaction mixture^ In the presence 

 of adenylic acid, both forms are equally active. Extracts of muscle and other tissues were 

 shown to contain an enzyme called PR (prosthetic group-removing) which converts 

 phosphorylase a to the b form^. It was at that time believed that phosphorylase a 

 contained firmly bound adenylic acid and that the PR enzyme removed it from the 

 protein. However, in 1944 it was stated that all attempts to demonstrate free adenylic 

 acid (or pentose) after PR action gave negative results^. Subsequent attempts to show 

 the presence of adenine in phosphorylase a were also unsuccessful^. 



Molecular changes of greater magnitude than removal of a prosthetic group have 

 recently been found to accompany the conversion of phosphorylase a to phosphorylase b. 

 A smaller protein, which can be identified as phosphorylase b, is formed in the reaction 

 catalyzed by PR. Sedimentation patterns in the ultracentrifuge show this second 

 molecular species to be absent from solutions of crystalline phosphorylase a but present 

 in all reaction mixtures in which conversion to phosphorylase b has occurred. 



The extent of conversion of phosphorylase a to phosphorylase b during PR action 

 is determined by assaying enzymic activity in the presence and in the absence of adenylic 

 acid. Results are expressed as % of specific activities (activity without/activity with 

 adenylic acid, X 100). From these data the relative proportions of the a and b forms of 

 phosphorylase in reaction mixtures have been calculated^ 



Fig. I A shows the sedimentation pattern of a 0.6% solution of phosphorylase a, 

 which is homogeneous in the ultracentrifuge. This preparation was 66% as active in the 

 absence as in the presence of adenylic acid. The activation of phosphorylase a by adenylic 

 acid would seem from this to be real and not due to contaminating phosphorylase b. 

 The sedimentation constant (S20, -J of phosphorylase a is 13.2 Svedberg units. 



Concomitant changes in ultracentrifugal and enzymic behavior when phosphorylase 

 a is incubated with the PR enzyme have been followed. Figs. iB, iC, iD, and lE show 



* Fellow of the National Institutes of Health, United States Public Health Service. This report 

 has been taken from a dissertation to be submitted by P- J- Keller in partial fulfilment of the 

 requirements for the degree of Doctor of Philosophy in Biological Chemistry, Washington University. 



References p. 238. 

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