Control of glycogen phosphorylase from mantle muscle of the cuttle fish, Sepia pharaonis
Thomas, T.P.; Philip, G.
Indian Journal of Biochemistry and Biophysics 20(4): 203-207
1983
ISSN/ISBN: 0301-1208 PMID: 6423521 Document Number: 206366
The control mechanism of glycogen phosphorylase (EC 2.4.1.1) from the mantle tissue of the cephalapod, S. pharaonis was different from that of the other animal phosphorylases. The enzyme exhibits negative homotropic cooperativity between AMP sites. Extracts of fresh Sepia mantle contain active phosphorylase phosphatase and phosphorylase kinase which become inactivated on freezing of the muscle. Rabbit muscle phosphorylase phosphatase and kinase do not intercovert the Sepia phosphorylase. Inhibition of the enzyme by glucose also is found to be different. Thus Sepia phosphorylase is structurally different. Although phosphorylase phosphatase and phosphorylase kinase are present in fresh mantle extracts, their role in controlling the activity of phosphorylase by interconverting the a and b forms appears to be insignificant because of the presencee of saturating concentrations of AMP in the mantle. The high energy demand of the mantle is met by maintaining a high concentration of AMP in the mantle muscle such that the enzyme is fully active whether it is present in the a or b form. Therefore, interconversion of the a and b forms does not appear to be a significant controlling factor of glycogen degradation, unlike in other cases studied so far. The special properties of the enzyme in relation to the evolutionary status of Sepia are discussed.