[Chemical reactivity of an essential arginine residue in substrate binding, reflecting the state of activation of glycogen phosphorylase in rabbit muscle].

Arginine residues have been shown to be present in the binding sites of both phosphorylated substrates and nucleotide activators of glycogen phosphorylase. The former residue can only be modified by arginine-directed reagents when the enzyme is activated, i. e. in phosphorylase a, or in phosphorylase b in the presence of activators. Conversely, after this residue has been modified, phosphorylase b is irreversibly blocked in an active conformation.