Human Liver Glycogen Phosphorylase. Kinetic Properties and Assay in Biopsy Specimens
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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.
Gibson R, Jeck W, Koch R, Mehta A, Choi S, Sriraman Y Mol Genet Metab. 2024; 143(4):108597.
PMID: 39488079 PMC: 11633833. DOI: 10.1016/j.ymgme.2024.108597.
Burrage L, Madan S, Li X, Ali S, Mohammad M, Stroup B JCI Insight. 2020; 5(4).
PMID: 31990680 PMC: 7101134. DOI: 10.1172/jci.insight.132342.
High frequency of missense mutations in glycogen storage disease type VI.
Beauchamp N, Taybert J, Champion M, Layet V, Heinz-Erian P, Dalton A J Inherit Metab Dis. 2007; 30(5):722-34.
PMID: 17705025 DOI: 10.1007/s10545-007-0499-9.
Mutations in the liver glycogen phosphorylase gene (PYGL) underlying glycogenosis type VI.
Burwinkel B, Bakker H, Herschkovitz E, Moses S, Shin Y, Kilimann M Am J Hum Genet. 1998; 62(4):785-91.
PMID: 9529348 PMC: 1377030. DOI: 10.1086/301790.
Radiochemical methods for the assay of phosphorylase in the direction of glycogenolysis.
Gevers G, Stalmans W Biochem J. 1981; 193(3):793-8.
PMID: 7305961 PMC: 1162668. DOI: 10.1042/bj1930793.