A novel inhibitor of glycogen phosphorylase from crayfish hepatopancreas

1. 1. A novel glycogen phosphorylase inhibitor was partially purified from crayfish hepatopancreas. 2. 2. The inhibitor was found only in two species of crayfish examined, and not in lobster, fresh and salt water clams, mussels or cockroaches. 3. 3. The inhibitor is a small protein (Mr = 23,000) which did not show proteolytic activity. 4. 4. Preliminary kinetic analysis of the inhibitory mechanism indicated that it bound to both glycogen and the glycogen phosphorylase protein. 5. 5. Inhibitor binding to glycogen resulted in a competitive inhibition pattern with respect to glycogen phosphorylase (inhibition constant of ca 10 μg/ml). 6. 6. The inhibitor also bound glycogen phosphorylase directly with a binding coefficient of 100 μg/ml resulting in a partially non-competitive inhibition pattern with respect to phosphate.

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