mcb450-19bs07

mcb450-19bs07 - Lecture 19b Glycogen Metabolism, Pentose...

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Lecture 19b Glycogen Metabolism, Pentose Phosphate Pathway, Photosynthesis Mintel Office Hours Today (4/5) 1:00-2:30, NL 208
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Glycogen Structure
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Glycogen Stores Liver Proximal tubule of the kidney Muscle
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Phosphorylase Reaction (Ch. 10) • (Glycogen) n glu + Pi = (Glycogen) n-1 glu + Glu 1-P
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Debranching Enzyme Removes all but one glucosyl residue from a branch point and transplants the short chain to a neighboring branch. This leaves a single glucosyl residue still to be removed.
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α 1,6-Glucosidase This removes the last glucosyl residue as glucose. Both this activity and debranching activity are present on the same protein molecule, a so-called tandem enzyme.
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Glycogen Breakdown
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Allosteric Effectors of Phosphorylase ATP, glucose 6-phosphate Inhibit phosphorylase 5′-AMP Activates phosphorylase
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Covalent Modification of Phosphorylase A serine residue on phosphorylase (a dimer) can be phosphorylated or dephosphorylated. The phsophorylated form is more active. The covalent modification is under hormonal control as is shown on the next slide.
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Hormonal Control Glucagon activates adenylyl cyclase through the G protein system, not indicated in this diagram for the sake of simplicity.
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cAMP
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G Proteins These are membrane proteins that relay hormonal signals to the interior of a cell. Typically glucagon and epinephrine bind to a cell surface receptor and activate a G protein. (Both glucagon and epinephrine stimulate glycogen breakdown.)
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G α with bound GTP is active in stimulating adenylyl cyclase. G
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mcb450-19bs07 - Lecture 19b Glycogen Metabolism, Pentose...

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