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  • Title: Human liver glycogen phosphorylase. Kinetic properties and assay in biopsy specimens.
    Author: Lederer B, Stalmans W.
    Journal: Biochem J; 1976 Dec 01; 159(3):689-95. PubMed ID: 1008826.
    Abstract:
    1. The two forms of glycogen phosphorylase were purified from human liver, and some kinetic properties were examined in the direction of glycogen synthesis. The b form has a limited catalytic capacity, resembling that of the rabbit liver enzyme. It is characterized by a low affinity for glucose 1-phosphate, which is unaffected by AMP, and a low V, which becomes equal to that of the a form in the presence of the nucleotide. Lyotropic anions stimulate phosphorylase b and inhibit phosphorylase a by modifying the affinity for glucose 1-phosphate. Both enzyme forms are easily saturated with glycogen. 2. These kinetic properties have allowed us to design a simple assay method for total (a + b) phosphorylase in human liver. It requires only 0.5 mg of tissue, and its average efficiency is 90% when the enzyme is predominantly in the b form. 3. The assay of total phosphorylase allows the unequivocal diagnosis of hepatic glycogen-storage disease caused by phosphorylase deficiency. One patient with a complete deficiency is reported. 4. The assay of human liver phosphorylase a is based on the preferential inhibition of the b form by caffeine. The a form displays the same activity when measured by either of the two assays.
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