title: Human liver glycogen phosphorylase. Kinetic properties and assay in biopsy specimens.
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.
mesh_terms: D000249:Adenosine Monophosphate; D000293:Adolescent; D002110:Caffeine / Q000494:pharmacology; D004789:Enzyme Activation; D005260:Female; D005459:Fluorides; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D006005:Phosphorylases / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000378:metabolism*; D013431:Sulfates
chemical_list: D013431:Sulfates; D002110:Caffeine; D000249:Adenosine Monophosphate; D006005:Phosphorylases; D005459:Fluorides