Pyridoxal phosphate-dependent conformational states of glycogen phosphorylase as probed by interconverting enzymes.

The interaction between pyridoxal 5'-phosphate and the convertible serine of glycogen phosphorylase has been investigated by using: specific interconverting enzymes, phosphorylase kinase and phosphorylase phosphatase; effectors, glucose and glucose 6-phosphate; and a protein kinase and trypsin. Both phosphorylase kinase and phosphorylase phosphatase utilized the native protein while having little influence on the apoprotein. Removal of a peptide containing the critical serine residue gave phosphorylase b' from which the pyridoxal 5'-phosphate in phosphorylase has an important effect on enzymic interconversion.