Purification and properties of the phosphorylase-rupturing enzyme

1955 Journal of Biological Chemistry  
Two forms of rabbit muscle phosphorylase were described by Cori and Green (1) in 1943: a euglobulin, phosphorylase a, having about 65 per cent of its maximal enzymatic activity without the addition of adenosine-5'phosphate, and a more soluble protein, phosphorylase b, which is enzymatically inactive unless adenylic acid is added to the reaction mixture. In 1945, Cori and Cori (2) described an enzyme from rabbit muscle which catalyzes the conversion of phosphorylase a to phosphorylase b. This
more » ... horylase b. This enzyme was designated the PR (prosthetic group-removing) enzyme in the belief that adenylic acid, firmly bound to phosphorylase a, was split out during conversion to phosphorylase b. However, all attempts to dcmonstrate this as the mechanism of the conversion reaction were unsuccessful. There was no evidence for the appearance of adenylic acid among the products of the conversion, nor for the presence of the nucleotide on phosphorylase a (2, 3). It was recognized in 1953 (4) that the conversion of phosphorylase a to phosphorylase b \vas associated with a near or exact halving in molecular weight, i.e. that the molecular changes effected by the PR enzyme were of a different nature than removal of a prosthetic group. It has been proposed, however, to retain the name PR (phosphorylase-rupturing) enzyme. The purification of rabbit muscle PR enzyme has been undertaken, and some of its properties have been studied. EXPERIMENTAL Estimation of Enzyme Activity-The method of assay described by Cori and Cori (2) has been used to measure PR activity. The conversion rcaction is followed by assay for phosphorylase activity under conditions in which only the a form is active, i.e. in the absence of added adenylic acid. That the disnppearnnre of phosphorylnse a is due t,o conversion to phosphorylase 1~ rather than to non-specific losses in activity can l)c rtstal~lislirtd * Postdoctoral Fellow of the United States Public Health Service. Present address,
pmid:14367370 fatcat:cpfrr6jcujewdfnw2nneyk6jdq