北大生化课件Chapter14.ppt
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1、Chapter 14 Glycolysis and the Pentose Phosphate Pathway Glycolytic pathway; Fermentation; substrate channeling; Pentose phosphate pathway.,To be lectured by Professor Zengyi Chang on September 19, 2007,The chemistry of glucose catabolism was elucidated over about 100 years,The anaerobic breakdown (f
2、ermentation) of glucose to ethanol and CO2 by yeast has been exploited for many centuries in baking and winemaking. Scientific investigation of the chemistry of glucose breakdown began in the mid-19th century. The complete pathway was described around 1940.,D-glucose occupies a central position in m
3、etabolism,NADPH +,(fat),Other biomolecules,The metabolic fates of glucose involves hundreds or thousands of chemical transformations.,CO2 + H2O,D-glucose,Go = 2840 kJ/mole,ATP,Biosynthesis,Understanding sugar catabolism occupied a central position in the development of biochemistry,Where cell-free f
4、ermentation with yeast extract was first observed by Buchner (1897): the vitalistic dogma was shaken and metabolim became chemistry. Where phosphorylated intermediates were first discovered (Harden and Young, 1900s). Heat-labile, nondialyzable enzymes were distinguished from the heat-stable, dialyza
5、ble coenzymes (e.g., NAD+). Muscle enzymes involved in the production of lactic acid were found to be astonishingly similar to the yeast enzymes involved in alcohol production. ATP was revealed to be an energy currency.,?,The whole pathway of glycolysis (arbitrarily defined as from glucose to pyruva
6、te) containing ten steps of chemical reactions with each catalyzed by a specific enzyme, was elucidated by the 1940s.,Glucose is first phosphorylated at C-6: consuming ATP,(Present in all cells of all organisms),Mg2+ATP2- is the actual substrate,An exergonic group transferring reaction,己糖激酶,Glucose
7、is thus trapped and destabilized.,Hexokinase exhibits induced fit property: The binding of glucose in the active site causes a major conformational change.,Inactive conformation,Active conformation,Glucose,Substrate-induced cleft closing is a general feature of all kinases!,Glucose 6-P is then conve
8、rted to fructose 6-P: via isomerization,A reversible Isomerization reaction (intramolecular redox reaction),An aldose,A ketose,磷酸己糖异构酶,A necessary prelude for the next two steps of reactions (phosphorylation and C-C cleavage).,Fructose 6-P is then phosphorylated at C-1: ATP consuming,Another exergon
9、ic group transferring reaction,(PFK-1),磷酸果糖激酶-1,The six-carbon fructose 1,6-bisphosphate is then cleaved into two different triose phosphates,The “lysis” step,1,2,3,4,5,6,醛缩酶,Interconversion between dihydroxyacetone phosphate and glyceraldehyde 3-P then occurs,(C3 or C4),(C5 or C2),(C1 or C6),Other
10、hexoses (e.g., Fru., Man., Gal.) are also converted to glyceraldehyde 3-phosphate to enter glycolysis.,A reversible Isomerization reaction (intramolecular redox reaction),磷酸丙糖异构酶,An aldose,A ketose,Glyceraldehyde 3-P is then oxidized to form 1,3-bisphosphoglycerate,Oxidation (dehydrogenation) follow
11、ed by phosphorolysis,An acyl phosphate (a type of anhydride),3-磷酸甘油醛脱氢酶,3H,32P,32P,3H,Tetrameric,A Cys residue is involved in the catalysis of glyceraldehyde 3-P dehydrogenase,Oxidation step,Phosphorolysis step,(An acyl-enzyme intermediate),Inactivation of the enzyme,NADH exchanged for NAD+,3-磷酸甘油醛脱
12、氢酶,HB,:B,HB,HB,The phosphoryl group linked to the carboxyl group of 1,3-bisphosphoglycerate is then transferred to ADP to form ATP,(This enzyme was named for the reverse reaction),substrate-level phosphorylation (vs. respiration-linked phosphorylation),磷酸甘油酸激酶,ADP,ATP,3-phosphoglycerate is then conv
13、erted to 2-phosphoglycerate,磷酸甘油酸变位酶,Mutase: catalyzes group transferring from one position to another in a molecule.,The phosphoglycerate mutase acts as a transient carrier of phosphoryl groups,Phosphoglucomutase acts in a similar fashion!,(Initially phosphorylated by using 2,3-BPG),2-phosphoglycer
14、ate is then dehydrated to produce phosphoenolpyruvate,A super high-energy phosphate compound,G0 for the hydrolysis of the phosphate group is changed from 17.6 to 61.9 kJ/mol.,烯醇酶,A Redistribution of energy,(PEP),The phosphoryl group of PEP is transferred to ADP to form ATP at the end,This enzyme was
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