7 糖代谢的其他途径 0.ppt

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1、Chapter13AdditionalPathwaysinCarbohydrateMetabolismGlycogendegradationandsynthesis糖原代谢与分解Gluconeogenesis糖异生ThepentosePhosphatepathway磷酸戊糖途径糖原的分解和生物合成一、糖原的分解二、糖原的生物合成三、糖原代谢的调控糖原(glycogen)，又称动物淀粉，支链，分子量数百万以上。主要由葡萄糖以α（1，4）糖苷键相连（93%)，以少量α（1，6）糖苷键（7%）形成分支。有肝糖原和肌糖原。糖原是由多个葡萄糖组成的带分枝的大分子多糖，分子

2、量一般在106-107道尔顿，可高达108道尔顿，是体内糖的贮存形式，糖原主要贮存在肌肉和肝脏中，肌肉中糖原约占肌肉总重量的1-2%约为400克，肝脏中糖原占总量6-8%约为100克。肌糖原分解为肌肉自身收缩供给能量，肝糖原分解主要维持血糖浓度。LiverBufferforregulatingbloodglucoselevelsMuscleStoreofglucoseasafuelforexercisehighintensityexercisedependentonanaerobicglycolysisGlycogenFunctions一、糖原的酶促磷酸解糖原

3、的结构及其连接方式磷酸化酶a（催化1.4-糖苷键断裂）三种酶协同作用：转移酶（催化寡聚葡萄糖片段转移）脱枝酶（催化1.6-糖苷键水解断裂）-1，4-糖苷键-1，6糖苷键非还原性末端Glycogenisapolymerofglucoseresidueslinkedbya(14)glycosidicbonds,mainlya(16)glycosidicbonds,atbranchpoints.Glycogenchains&branchesarelongerthanshown.Glucoseisstoredasglycogenpredominantlyinli

4、verandmusclecells.GlycogenDegradationGlycogenPhosphorylaseHydrolyzesglucoseunitsfromglycogenProducesglucose-1-PRemovalofbranchpointsDebranchingenzymecomplexGlucantransferaseAlpha-1,6-glucosidaseGlycogenPhosphorylasecatalyzesphosphorolyticcleavageofthea(14)glycosidiclinkagesofglycoge

5、n,releasingglucose-1-phosphateasreactionproduct.glycogen(nresidues)+Piglycogen(n–1residues)+glucose-1-phosphateThisphosphorolysismaybecomparedtohydrolysis:Hydrolysis:R-O-R'+HOHR-OH+R'-OHPhosphorolysis:R-O-R'+HO-PO32-R-OH+R'-O-PO32-Glycogencatabolism(breakdown):Aglycogenstoragesite

6、onthesurfaceofthePhosphorylaseenzymebindstheglycogenparticle.Giventhedistancebetweenstorage&activesites,Phosphorylasecancleavea(14)linkagesonlytowithin4residuesofana(16)branchpoint.Thisiscalleda"limitbranch“.Debranchingenzymehas2independentactivesites,consistingofresiduesindifferen

7、tsegmentsofasinglepolypeptidechain:Thetransferaseofthedebranchingenzymetransfers3glucoseresiduesfroma4-residuelimitbranchtotheendofanotherbranch,diminishingthelimitbranchtoasingleglucoseresidue.Thea(16)glucosidasemoietyofthedebranchingenzymethencatalyzeshydrolysisofthea(16)linkage,

8、yieldingfree