Mechanism of allosteric activation of glycogen phosphorylase probed by the reactivity of essential arginine residues. Identification of an arginine residue involved in the binding of glucose 1-phosphate

Publisher Website
Google Scholar
Abstract
The physicochemical and kinetic properties of [rabbit muscle] glycogen phosphorylase modified by arginine-specific reagents under different conditions were previously reported. The properties of the modified enzyme depend upon the conformation adopted by the enzyme during the modification reaction. In this paper, the localization of the crucial modified arginine residues on the primary structure is reported. The chymotryptic peptide extending from residue Asp-563 to residue Tyr-572 was shown to contain 1 arginine residue (Arg-568) which is chemically modified by phenylglyoxal in phosphorylase a and in activated phosphorylase b. Inclusion of glucose 1-phosphate in the modification medium protects this residue from modification, with a concomitant protection of the enzyme activity. This residue is not reactive toward phenylglyoxal in phosphorylase b in the absence of any effector. Addition of the AMP analog 2''dAMP, which is not an activator of the enzyme, does not increase Arg-568 reactivity, but protects from modification several arginine residues located between Arg-242 and Leu-348. The location and the role of Arg-568 in phosphorylase are discussed with reference to recent data from X-ray crystallography.