Term
| 2 interconvertible forms in which the glycogen phosphorylase of skeletal muscle exists (discovered by Carl & Gerty Cori in the late 1930s) |
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Definition
1. glycogen phosphorylase a (catalytically active)
2. glycogen phosphorylase b (less active) |
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Term
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Definition
| initiated by elevated [cAMP]; a catalyst activates a catalyst which activates a catalyst |
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Term
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Definition
| activated & phosphorylated by PKA; catalyzes the phosphorylation of Ser residues in each of the two identical subunits of glycogen phosphorylase which activates it & stimulates glycogen breakdown |
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Term
| phosphorylase a phosphatase (phosphoprotein phosphatase 1) (PP1) |
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Definition
| an enzyme that becomes active when the muscle returns to rest; removes the phosphoryl groups from phosphorylase a which converts it to the less active form (phosphorylase b) |
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Term
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Definition
| converted from glycogen synthase a by phosphorylation of the hydroxyl side chains of several Ser residues of both subunits; is inactive unless its allosteric activator (glucose 6-phosphate) is present |
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Term
| glycogen synthase kinase 3 (GSK3) |
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Definition
| the most important regulatory kinase; adds phosphoryl groups to three Ser residues near the carboxyl terminus of glycogen synthase which strongly inactivates it |
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Term
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Definition
| integral to the hierarchal action of GSK3; GSK3 cannot phosphorylate glycogen synthase until this protein kinase has first phosphorylated the glycogen synthase on a nearby residue (this event is called priming) |
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Term
| glycogen-targeting proteins |
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Definition
| a family of proteins that tightly binds phosphoprotein phosphatase 1 to its target proteins so that it does not exist free in the cytosol; bind glycogen & each of the three enzymes glycogen phosphorylase, phosphorylase kinase, & glycogen synthase |
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