THE MUSCLE PHOSPHORYLASE b KINASE REACTION

The conversion of skeletal muscle phosphorylase b to phosphorylase a is catalyzed by an enzyme requiring ATP' and a divalent metal (1).In this reaction phosphate is transferred from the nucleotide to phosphorylase, and a dimerization of the enzyme occurs (2).The dimer-monomer relationship existing between phosphorylases a and b was noted originally by Keller and Cori in their work on the phosphorylase a to b reaction (3).In liver an inactive form2 of phosphorylase exists, which in a similar manner may be transformed to active phosphorylase by a process involving phosphorylation of the protein (4, 6).With the liver enzyme no dimerization of the molecule was noted.By using crystalline phosphorylase b ( 7) it has been possible to obtain quantitative data with reference to the number of moles of phosphate introduced per mole of phosphorylase a and to determine the nature of the nucleotide product in the phosphorylase b to a conversion.The equation for the reaction can be written as follows:No evidence for the reversibility of this reaction has been noted.The conversion of phosphorylase b to a by the above reaction can be catalyzed by traces of converting enzyme and serves as a convenient method for the preparation of crystalline phosphorylase a starting with the readily obtainable phosphorylase b (7). Methods Mate&&-Phosphorylaseb kinase and crystalline phosphorylase b were prepared by methods described previously (2, 7).A-R-P-P32-P32 was pre-