Glycogen Synth and Degrad

Glycogen Synth and Degrad - Glycogen Synthesis and...

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Glycogen Synthesis and Degradation if too little carbohydrate is supplied by the diet, glycogen reserves in liver and muscle tissue are mobilized Regulation of Glycogen Degradation o α-amylase (saliva, pancreatic secretions) – endoglcosidase; hydrolyzes α-1,4 linkages of glycogen and amylopectin; produce maltose, maltotriose, and small oliogsaccharides; leaves small highly branched saccharides (stops 4 residues away from any branching point) limit dextrins –highly branched polysaccharides left after α- amylase exposure; degraded by debranching enzymes glucanotransferase activity: transfer of trisaccharide unit from one branch to the end of another (α-amylase can act on this) glucosidase activity: hydrolyzes α-1,6 branch points o Digestion: highly efficient; unregulated (both catabolic and anabolic enzymes present in glycogen granules); thus, synthesis and degradation of storage glycogen must by highly regulated o Dietary and storage glycogens are digested through different pathways o Glycogen Phosphorylase – main enzyme of glycogen catabolism; cleaves 1 sugar unit from end of glycogen chain and uses P i to phosphorylate the glucose (avoids spending ATP to phosphorylate glucose) ; produce limit dextrins rxn is called phophorolysis b/c glycosidic bond is split by phosphate; ΔG = ~ 6 kJ/mol (b/c P i is in excess compared to glu-6- P in muscle, glu-6-P enters glycolysis; in liver, it’s hydrolyzed to glu to be transported to other tissues structure: 2 identical subunits w/ active and allosteric effector sites and towers; regulated by allosteric mechanism and covalent modification
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o P i is positive homotropic effector
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Glycogen Synth and Degrad - Glycogen Synthesis and...

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