BBMB 405 1nd Edition Lecture 7 Jan 28Outline of Last Lecture VII. Chapter 20: The Calvin Cycle and the Pentose Phosphate PathwayE. Glucose 6-phosphate Dehydrogenase plays key role in protection against reactive oxygen speciesX. Handout (1/23)XI. Handout (1/26)XII. Chapter 21: Glycogen MetabolismA. Glycogen Breakdown requires the interplay of several enzymesB. Phosphorylase is regulated by allosteric interaction and reversibleOutline of Current Lecture XII. Chapter 21: Glycogen MetabolismC. Epinephrine and glucagon signal the need for glycogen breakdownD. Glycogen is synthesized and degraded by different pathwaysE. Glycogen breakdown and synthesis are reciprocally regulatedCurrent LectureX. Chapter 21: Glycogen MetabolismC. Epinephrine and glucagon signal the need for glycogen breakdown1. G proteins transmit signal for initiation of glycogen breakdowna. Hormonal regulation of glycogenolysis (trigger glycogenolysis)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. Glucagon (fasting/low blood sugar level): pancreas releases glucagon, glucagon receptors on liver membraneii. Epinephrine (in response to exercise): released from adrenal gland, beta receptors on muscle cells (major glycogen breakdown), alpha receptors on liver cellsiii.iv. Amplification process/Regulatory cascade for glycogen breakdown(primarily in muscle)A. Signal molecules (epinephrine or glucagon) bind to 7TM receptor, specific external signal is transmitted into cell through structural changesB. GTP bound to receptor then activates adenylate cyclase which catalyzes formation of cAMP from ATPC. cAMP activates protein kinase A, cAMP activates protein kinase A (PKA): R2C2 (Inactive) –4cAMP 2R-cAMP2 + 2C (active)D. Protein kinase A phosphorylates phosphorylase kinase which activates glycogen phoshporylaseE.v. Liver: phosphoinositide cascadeb. Intracellular messengersi. cAMP: glucagon receptor and beta receptorii. Ca++: alpha receptor (used in phosphoinositide cascade in liver)2. Glycogen breakdown must be rapidly turned off when necessarya. So we don’t breakdown all the glycogen it is regulatedb. When hormone is no longer present glycogen phosphorylase is automatically shut downc. All activated molecules turn back to inactive forms (AMP, GDP, phosphorylase kinase – 1 phosphoryl group, glycogen phosphorylase b)3. Regulation of glycogen phosphorylase became more sophisticated as enzyme evolvedD. Glycogen is synthesized and degraded by different pathways1. UDP-glucose is activated form of glucosea. Synthesis: Glycogenn + UDP-Glucose  glycogenn+1 + UDPb. Degradation: Glycogenn+1 + Pi  glycogenn + glucose 1-phosphatec. UDP-Glucose: adds glucose on to non reducing end of glycogen, is activated form of glucosed. Reaction catalyzed by UDP-glucose pyrophosphorylasee.f. Note: theme in biochemistry is many biosynthetic reactions are compelled by hydrolysis of pyrophosphate2. Glycogen synthase catalyzes transfer of glucose from UDP-glucose to growing chaina. Linkage is made at C4 of terminal residue forming an alpha-1,4-glycosidic linkageb. Reaction catalyzed by glucogen synthase which is a key regulatory enzymewhen building glycogenc.d. Glycogen synthesis needs a primer because it can only add glucosyl residue to chain that contains more than four residues: glycogenine. Glycogen synthesis (handout 1/28)i. Glycogenin (2 subunits) + 16 UDPG –auto-glucosylation onto tyrosine (Glucose)8-Glycogenin-(Glucose)8 –(conversion of nUDPG to nUDP) Glycogenii. (Glucose)8-Glycogenin-(Glucose)8 is basic building block of glycogen3. A branching enzyme forms alpha-1,6 linkagea. Glycogen synthase only makes alpha alpha-1,4 linkages and branching enzymes forms alpha-1,6 linkageb. Branch reacted by breaking alpha-1,4 linkage and forming an alpha-1,6 link (different from debranching)c. Conditions: at least 7 glucose units transferred, attached at least 4 glucose units away from other branch, chain must have at least 11 unitsd.e. Branching increases solubility of glycogen (important), branching also increases rate of glycogen synthesis and degradation4. Glycogen synthase is key regulatory enzyme in glycogen synthesisa. Covalent modification: Phosphylationi. Changes lead to inactivation: Glycogen synthase kinase (GSK), Protein kinase Aii. Activation: glycogen synthase, phosphorylaseb. Allosteric regulation: activate phosphorylase b with high levels of glucose 6-phosphate5. Glycogen is efficient storage form of glucosea. Synthesis of glycogen is very efficient, only requires 1 ATP and if make 31 ATP per glucose is 97% efficientb.E. Glycogen breakdown and synthesis are reciprocally regulated1. “The same glucagon- and epinephrine-triggered cAMP cascades that initiate glycogen breakdown in liver and muscle, respectively, also shut off glycogen synthesis. Glucagon and epinephrine control both glycogen breakdown and glycogen synthesis through protein kinase A.” (Biochemistry p. 630)2. Protein phosphatase 1 reverses regulatory effects of kinase on glycogen metabolisma.b. Protein phosphatase 1 is key in regulating glycogen metabolism, it inactivates phosphorylase a and phosphorylase kinase, activates glycogensynthase by removing phosphoryl groups, activated by insulin (insulin increases glycogen synthesis)c. Glycagon and epinephrine stimulate glycogenolysis and control activity of protein kinase A and slows down PP1 activityd. Regulatory subunits bound to catalytic subunits: GM in heart and muscle, GL in liver, “Regulatory subunits act as scaffolds, bringing together phosphatase and its substrates in context of glycogen particle.” (Biochemistry p. 631)e.3. Insulin stimulates glycogen synthesis by inactivating glycogen synthase kinasea. Insulin binds to receptor tyrosine kinase and activates it to phosphorylate insulin-receptor substrates (IRSs) which trigger pathways that lead to activation of protein kinases that inactivate glycogen synthase kinase, kinase can not longer maintain glycogen synthase so PP1 dephosphorylates glycogen synthase and activates it and restoring glycogen reserves. (net effect of insulin: replenishment of glycogen stores)b.4. Glycogen metabolism in liver regulates blood-glucose levela.b. Conversion of a into b is accompanied by release of PP1 which then is freeto activate glycogen synthase and dephosphorylate glycogen phosphorylasec. Activity of glycogen synthase only increases after most of