Human biochemistry, Medical Biotechnology, inglese

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Glycogen sinthase

related!to!Glucose.!! In! fasting! condition! the! enzyme! is! in! the! form! Phosphorylase1 a! that! is! phosphorylated/and/

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Enzymatic

Glucose!is!converted!into!Glucose;6P!to!be!converted!into!Glycogen,!to!enter!the!Krebs!cycle! active:!the!binding!of!Glucose!to!an!allosteric!site!induces!a!conformational!change!that!causes!

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or!the!shunt.! the!exposition!of!two!phosphorylated!Ser!residues!that!are!rendered!available!for!the!activity!

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Glucose;6P!produced!by!gluconeogenesis!or!by!glycogenolysis!must!be!converted!into!Glucose! of!the!Protein/Phosphatase/1!(PP1)!that!removes!the!P!group!giving!the!form!Phosphorylase1

Glycogen phosphorylase

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(if!Glucose!has!to!move!from!liver!to!other!tissues)!by!GlucoseO6P/phosphatase.!! b!that!is!the!less/active/form/of/the/enzyme.! d

Glucose inhibits glycogen phosphorylase and facilitates

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2 4 6 8 10

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! ! protein phosphatase activity gl

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This!enzyme!is!associated!to!the!ER,!it!has!a!Km!for!Glucose;6P!of!2;3!mM.! de

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Glucose;6P!concentration!in!the!cell!can!vary!between!0,05;1!mM,!and!the!first!control!of!the! Glucose inhibits glycogen phosphorylase and facilitates

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enzyme! is! on! the! concentration! of! its! substrate:! only! when! Glucose! reaches! 1mM! Glu;6P! protein phosphatase activity

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Phosphatase!can!work!at!its!high!maximum!capacity.!! si

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The!structure!is!characterized!by!the!presence!of!His!and!Arg!residues!in!the!catalytic!domain! PP1

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that!faces/the/luminal/environment.!The!enzyme!has!also!a!TM!domain!and!the!N;terminal!is! Un !

luminal!while!the!C;terminal!cytoplasmic.! ! iv PP1

! After! the! dephosphorylation,! PP1! can! exert! its! activity! on! Glycogen! Synthase:! PP1! removes!

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The!enzyme!works!with!a!covalent/modification:!! the! P! group! on! the! Glycogen1 Synthase1 b! (inactive/form)! and! converts! it! into! the! Glycogen1

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1. Transfer!of!the!P!on!His! Synthase1a!(active/form)!determining!the!activation!of!the!enzyme.!!

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2. Hydrolysis!of!the!P!group!from!His!that!is!then!transferred!to!Arg! PP1

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py Glycogen Glycogen

synthase b synthase a

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Co Glycogen Glycogen

synthase b synthase a !

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Regulation/of/Glycogen/metabolism/

How!can!these!activities!be!coordinated?!The!coordination!and!the!sequential!activity!of!PP1!

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For!the!activity!of!Glucose;6P!Phosphatase!in!the!ER!the!cell!need!a!transporter!for!Glu;6P,!for! and! the! two! enzymes! depends! on! the! structure! of! the! Glycogen/ granule:! all! the! proteins!

Glucose!and!for!the!P!group.! involved!in!Glycogen!metabolism!are!strictly!associated!to!Glycogen!granules!and!organized!in!

The!enzyme!is!regulated!by:!glucocorticoids/and/cAMP!and!it!is!negatively!regulated!by!insulin.! super!protein!complexes!containing:!

The! main! regulation! of! the! enzyme! is! based! on! the! substrate/concentration! (a! part! from! the! ; Glycogen/Phosphorylase/

transcriptional!regulation).! ; Glycogen/Synthase/

! ; Protein/Phosphatase/1/

6.2.17! ; Adaptor/protein/G /

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Well6fed1state:1Glucose1storage16mg/Kg/min1 So! PP1! can! work! on! Glycogen! Phosphorylase! and! once! dephosphorylated! it,! it! can! work! on!

The!amount!of!hepatic!Glycogen!is!about!70gr!in!an!adult!male!of!about!70Kg,!if!you!consider! Glycogen! Synthase! and! the! organization! of! the! protein! complex! allows! this! sequential! PP1!

that!liver!is!about!1,5Kg!the!concentration/of/Glycogen/in/liver/is/the/higher/in/the/body,!while!in! activity.!

muscles!is!less!than!in!liver!even!if!the!total!amount!of!muscle!Glycogen!is!higher.! !

Liver/Glycogen/concentration/undergoes/in/vary/rapid/changing/from/the/concentration/of/10gr/ Insulin! can! promote! to! the! phosphorylation! of! the! two! enzymes! because! it! can! activate! an!

glucose is the signal to swhitch the glycogen

per/100gr/in/the/wellOfed/state/to/0,3/0,5gr/per/100gr/in/fasting/condition! and/during/exercise,! insulin;sensitive!kinase!which!can!phosphorylates!the!adaptor!protein!G .!

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metabolism from degradation to synthesis

because!liver!Glycogen!can!support!the!activity!of!skeletal!muscles.!! G !has!two!sites!of!phosphorylation!that!can!be!phosphorylated!by!two!different!proteins:!

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! Insulin6sensitive1kinase!→!Insulin!binds!to!its!receptor!and!induces!the!activation!of!

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M How!can!this!variation!be!regulated?!Glucose!represents! a!kinase!that!phosphorylates!G .!

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the! signal! to! switch! the! Glycogen! metabolism! from!

activity G ;P!maintains!the!architecture!of!the!complex!and!thus!stimulates/the/activity/of/PP1.!!

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Glycogen sinthase M

d degradation! to! synthesis:! in! the! graph! you! can! see! that! PKA! the! PKA! can! be! activated! by! Glucagon:! the! further! phosphorylation! (2P)!

Enzymatic • →!

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ud the! enzymatic! capacity! of! Glycogen! Phosphorylase! induces!the!detachment!of!G !from!the!complex.!This!allows!the!release!of!PP1!that!is!

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decreases! when! Glucose! in! the! liver! increases,! and! only! no! more! active! on! the! enzymes! (PP1! is! active! only! when! associated! to! the! complex)!

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Glycogen phosphorylase when!Glycogen!Phosphorylase!activity!is!at!the!minimum! thus!promoting!the!phosphorylation!of!the!two!enzymes.!!

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i there!is!a!sharp!increase!in!Glycogen!synthesis.!! !

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Glucose inhibits glycogen phosphorylase and facilitates

 protein phosphatase activity

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iv PP1

Un During! fasting/ condition! PKA! determines! also! the!

phosphorylation! of! inhibitor1 1! a! scaffold! protein!

that! maintains! PP1! far! from! the! granules! when! it! is!

phosphorylated.!!

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Glycogen! Synthase! can! be! phosphorylated! by!

different! kinases,! in! particular! GSK3! (Glycogen/

Regulation of glycogen metabolism

Synthase/ Kinase/ 3):! GSK3! can! phosphorylate! the! o

Glycogen!Synthase!inhibiting!it.! n !

GSK3! can! be! inactivated/ by/ Insulin! through! the!

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PI3K! pathway! that! activates! PKB! (Akt):! PKB! can! Glucose!is!phosphorylated!in!Glu;6P!that!can!be!used!to!restore!Glycogen!in!the!liver.!

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phosphorylate!GSK3!inactivating!it.!! Than!Glu;6P!can!be!addressed!to!glycolysis!and!produce!Pyruvate!which!can!be!internalized!

So! when! GSK3;P! is! inactive,! PP1! is! active! and! in!the!mitochondria!where!it!is!converted!into!Acetyl;CoA.!

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Glycogen!Synthase!can!be!activated.! Acetyl;CoA!is!condensed!with!Oxaloacetate!giving!rise!to!the!formation!of!Citrate.!!

! di Citrate!has!two!possibilities:!

! tu ; Be!converted!in!the!Krebs!cycle!

! ; The!amount!of!Citrate!over!the!possibility!of!Krebs!cycle!moves!from!the!mitochondria!

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! to! the! cytoplasm:! Citrate! is! converted! into! Acetyl;CoA! and! this! is! the! way! to! transfer!

Glucose! and! Glu;6P! stimulate! the! activity! of! PP1;! in! particular! Glu;6P! acts! as! an! allosteric!

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gl Acetyl;CoA!to!the!cytoplasm!(and!this!is!the!condition!active!in!the!liver!during!well;

regulator!which!binds!to!Glycogen!and!promotes!its!dephosphorylation!by!PP1.! fed!state).!!

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Glucagon!and!epinephrine!act!exactly!in!the!opposite!way:!they!block!the!activity!of!PP1!on! Citrate!is!then!activated!into!Malonil;CoA!that!is!used!to!synthetize!Acyl;CoA!that!can!

Glycogen sinthase is a substrate for different kinases

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Glycogen!Synthase,!inactivating!it.! then!be!used!for!the!synthesis!of!Triglycerides.!!

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si Glycolysis! can! also! produce! Glycerol;3P! through! the! reduction! of! Glyceraldheyde;3P,! a!

r glycolysis! intermediate.! Glycerol! that! reaches! the! liver! from! the! adipose! tissue! can! also! be!

ve phosphorylated! by! a! Glycerol! Kinase! in! the! liver;! so! we! have! the! possibility! to! synthesize!

i Triglycerides.!

Un For!the!biosynthesis!of!Acyl;CoA!we!also!need!reducing!equivalents:!the!reducing!equivalents!

are!generated!by!the!oxidation!of!Glucose;6P!in!the!Pentose!pathway.!!

ht So!the!two!pathways!are!integrated!because!the!main!aim!of!Pentose!pathway!is!to!produce!

ig NADPH!(in!this!condition!we!don’t!need!Ribose;5P).!

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How!these!two!pathways!can!be!controlled!in!the!wellOfed/state?!

p The! fundamental! steps! that! control! glycolysis! are! the! reactions! driven! by!

Co ! Phosphofructokinase!(PFK!I)!and!Pyruvate!kinase.!

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In! the! well;fed! condition! Glycogen! Synthase! is! activated! and! Glycogen! Phosphorylase! is! !

inhibited.! !

The! first! event! in! this! switching! is! due! to! the! action! of! Glu;6P,! but! there! are! two! other! !

metabolic!pathways!that!are!activated!in!the!storage!of!Glucose:! !

; Pentose/ pathway→! associated! to! the! production! of! the! reducing/ equivalents! for! the! !

Fatty!Acids!synthesis! !

; Glycolysis!→!more!strictly!assessed!to!the!synthesis!of!Fatty!Acids!because!the!goal!is!to! !

generate!Pyruvate!and!then!Acetyl;CoA!that!is!largely!used!for!the!synthesis!of!FA.!

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! The!positive/control!is!exerted!by!F1,6BP!that!is!an!upstream!substrate!of!the!enzyme!which!!

Phosphofructokinase611 can! give! a! message! of! the! need! of! an! increase! in! the! Pyruvate! kinase! activity.! All! these!

Phosphofructokinase I

The! most! important! regulatory! molecule! for! PFK! I! is! mechanism!are!active!in!all!glycolytic!tissues!including!liver.!

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Fructose62,66BP:! this! molecule! activates! the! PFK;1! and! !

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inhibits! the! FPBase;1! (that! is! the! enzyme! of! But! there! is! a! mechanism! specific/ for/ liver,! in! which! the! enzyme! can! be! inhibited! by!

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gluconeogenesis),!exerting!an!opposite!effect.! phosphorylation.!The!isoenzyme!Pyruvate!kinase!L!present!in!the!liver!is!inactive!in!its!P;form!

When! Fructose;2,6;BP! increases,! glycolysis! is! activated! and!the!phosphorylation!can!be!achieved!by!the!activity!of!PKA;!the!removal!of!the!P;group!by!

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and! gluconeogenesis! is! inhibited,! so! the! control! depends! the! phosphatases! PP1! or! PP2A! can! convert! Pyruvate! kinase! in! the! active! form!

on!the!levels!of!Fructose;2,6;bP! (dephosphorylated!).!!

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! When/ Insulin/ is/ high,/ PP1/ is/ active/ and/ the/ enzyme/ is/ dephosphorylated/ and/ active;/ when/

! Glucagon/is/high,/the/enzyme/is/phosphorylated/and/so/inactive.//

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The! enzyme! activities! that! regulate! the! level! of! Fatty1Acids1biosynthesis1

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F2,6BP!are!in!the!same!protein:!it!is!a!Kinase!that! Glycolysis!can!increase!the!level!of!Acetyl;CoA!that!is!then!used!for!the!synthesis!of!FA.!!

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works!on!position!2!of!the!Fructose;6P,!but!it!also! Which!are!the!proteins!involved!in!this!Fatty!Acids!biosynthesis?!

has! a! Phosphatase! activity! on! the! same! group! The! first! one! is! the! enzyme! that! activates! Acetyl;CoA! to! the! condensation! step:! Acetyl6CoA1

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(while!PFK1!phosphorylates!in!position!1,!it!is!the! Carboxylase! is! an! ATP! and! biotinOdependent! enzyme! that! catalyses! the! carboxylation! of!

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enzyme!active!in!glycolysis).! Acetyl;C