Purification of glycogen phosphorylase b from AMP-aminohydrolase activity

The presence of AMP aminohydrolase (EC 3.5.4.6) activity in glycogen phosphorylase b (EC 2.4.1.1) preparations, suggested by L. N. Johnson, N. B. Madsen, J. Mosley, and K. S. Wilson (1974, J. Mol. Biol.90, 703–717), has been confirmed in our laboratory. Since the hydrolase catalyzes the conversion of AMP into IMP the presence of traces of this impurity would dramatically affect, and could even invalidate, the results concerning some studies on the phosphorylase b-AMP interaction. The incubation of the phosphorylase b preparations with alumina Cγ in the cold for a brief period of time is proposed as a simple method of efficiently eliminating this impurity.