Chapter 11: GlycolysisChapter 11: Glycolysis

“Enjoy the chemical elegance of metabolism”

amylose sucrose lactose glucose fructose

-oseamylase

-ase disaccharides

Active transport passive transport

Low [Glc] High [Glc] Low [Glc]

Chapter 11: GlycolysisChapter 11: Glycolysis

Net Reaction:Glucose + 2 ADP + 2 NAD+ + 2 Pi 2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O

1-4 = hexose (6C) stage: 2 ATP’s consumed.5-10 = triose 2(3C) stage: 4 ATP’s produced. Net: 2 ATP’s.

Defined: Glucose is converted anaerobically to the three carbon acid pyruvate (only top half diagram)

Max energy when pyruvate from glycolysis enters Citric Acid Cycle Makes reducing eqivalents NADH and QH2 (FADH2)

Glucose

Glucose-6-phosphate

Fructose-6-phosphate

Fructose-1,6-bisphosphate

Dihydroxyacetone phosphate

Glyceraldehyde-3-phosphate

1,3-bisphosphoglycerate

3-phosphoglycerate

2-phosphoglycerate

phosphoenolpyruvate

pyruvate

Glyceraldehyde-3-phosphate

1,3-bisphosphoglycerate

3-phosphoglycerate

2-phosphoglycerate

phosphoenolpyruvate

pyruvate

Hexokinase

Glucose-6-phosphate isomerase

Phosphofructokinase-1

Trios phosphate isomerase

Aldolase

Glyceraldehyde-3-phosphate dehydrogenase

Phosphoglycerate kinase

Phosphoglycerate mutase

Enolase

Pyruvate kinase

ATP

ADP

ATP

ADP

ADP

ATPADP

ATP

ADP

ATPADP

ATP

NADH + H+

NAD+ + Pi

NADH + H+

NAD+ + Pi

H2O H2O

Phosphorylation

Phosphorylation

Substrate Level Phosphorylation

Substrate Level Phosphorylation

Oxidation and Phosphorylation

Isomerization

Cleavage

Isomerization

Rearrangement

Dehydration

The Pathway

Glycolysis: Step 1, HexokinaseGlycolysis: Step 1, Hexokinase

Can’t leave the cell

I-III IV

Isozymes Different inhibition profiles Location, Km Control point

C-6

Glycolysis: Step 2Glycolysis: Step 2Glucose 6-Phosphate IsomeraseGlucose 6-Phosphate Isomerase

Stereospecific: uses -Glc; produces -D-fructose-6-phosphate

Opens the chainduring the rxn

Aldose

Ketose

CH2OH

OH

Step 3, Phosphofructokinase-1Step 3, Phosphofructokinase-1

Metabolically irreversible rxn. It is an allosteric enzyme and a REGULATory CONTROL step for glycolysis (AMP and citrate).

PFK-1

First COMMITted step of glycolysis

Phosphofructokinase-1

Other 6-C sugars can enter and convert to fru-6-phos fructose, mannose, etc.

-anomer

Glycolysis: Steps 2 and 3Glycolysis: Steps 2 and 3

Stereospecific: uses -Glc; produces 100% -D-fructose-6-phosphate

Opens the chainduring the rxn

PFK-1

utilizes 100% -anomer

36% -fructose 64% -fructose

CH2OH

OH

Glycolysis: Step 4, AldolaseGlycolysis: Step 4, Aldolase

123

456

Rxn is near equilibrium, so not a control pointBasic residue or metal withdraws an

e- polarizing C2 carbonyl

Basic residue removes a proton from the C4 hydroxyl group

Rapid depletion of 2 products in subsequent steps drives rxn

Fig 11.5 Mech

Step 5, Triose Phosphate IsomeraseStep 5, Triose Phosphate Isomerase

Only G3P, not DHAP, can be utilized in step 6 Now have 2 molecules G3P for step 6

Consumption in step 6 maintains steady state conc. of G3P

Ketose-aldose conversion is diffusion controlled

After conversion, C-1=C-6, C-2=C-5, C-3=C4 (see textbook)

near equil.

AldoseKetose

Step 5, Triose Phosphate IsomeraseStep 5, Triose Phosphate Isomerase

near equil.

AldoseKetose

Glycolysis: Step 6Glycolysis: Step 6Glyceraldehyde 3-Phosphate DehydrogenaseGlyceraldehyde 3-Phosphate Dehydrogenase

Oxidation has neg G, some energy conserved in acid anhydride linkage

Oxidation is coupled to phosphorylation to conserve energy, instead of oxidation to free carbonic acid and energy loss

Higher group transfer potential than ATP

from Pi

Step 7, Phosphoglycerate KinaseStep 7, Phosphoglycerate Kinase

Near equilibrium rxn. Reversibility is important for reverse step in glucose synthesis (gluconeogenesis).

Really steps 6&7 couple oxidation to phosphorylation of ADP

Substrate level phosphorylation- Nucleotide diphosphate phosphorylated Donor is not a nucleotide

First ATP generating step

Glycolysis: Step 8, Phosphoglycerate Glycolysis: Step 8, Phosphoglycerate MutaseMutase

iPGM-cofactor independant

dPGM-cofactor dependant

Step 9, EnolaseStep 9, Enolase

phosphomonoester

Enol-phosphate ester

PEP: Very high P-group transferpotential

Glycolysis: Step 10, Pyruvate KinaseGlycolysis: Step 10, Pyruvate Kinase

2nd sub level phosphorylation

3rd metabolically irreverible rxn

Reg allosteric and covalent modification

Glucose

Glucose-6-phosphate

Fructose-6-phosphate

Fructose-1,6-bisphosphate

Dihydroxyacetone phosphate

Glyceraldehyde-3-phosphate

1,3-bisphosphoglycerate

3-phosphoglycerate

2-phosphoglycerate

phosphoenolpyruvate

pyruvate

Glyceraldehyde-3-phosphate

1,3-bisphosphoglycerate

3-phosphoglycerate

2-phosphoglycerate

phosphoenolpyruvate

pyruvate

Hexokinase

Glucose-6-phosphate isomerase

Phosphofructokinase-1

Trios phosphate isomerase

Aldolase

Glyceraldehyde-3-phosphate dehydrogenase

Phosphoglycerate kinase

Phosphoglycerate mutase

Enolase

Pyruvate kinase

ATP

ADP

ATP

ADP

ATP

ADP

ATP

ADP

ATP

ADP

ATP

ADP

NADH + H+

NAD+ + Pi

NADH + H+

NAD+ + Pi

H2O H2O

Phosphorylation

Phosphorylation

Substrate Level Phosphorylation

Substrate Level Phosphorylation

Oxidation and Phosphorylation

Isomerization

Cleavage

Isomerization

Rearrangement

Dehydration

Three Metabolically Irreversible Reactions

#3

#10

#1

Most are near equilibrium

Energetics of GlycolysisEnergetics of Glycolysis

**** **

1. Hexokinase3. Phosphofructokinase 110. Pyruvate Kinase

Few large -G steps, irreversible, regulated

Most are near equilibrium and have G close to zero

Steps 2, 4, 5, 6, 7, 8, 9

Enter the Le Chatelier

Physiological Regulation of GlycolysisPhysiological Regulation of Glycolysis

Insulin Independent UptakeBrainLiverRed Blood Cells

Insulin Dependent UptakeMuscleAdipose

Hormones InvolvedHigh blood [Glc], insulin releasedLow blood [Glc], glucagon released

Regulation of Glycolysis by Cellular ImportRegulation of Glycolysis by Cellular Import

[Glucose] high in bloodsteam and low inside most cells- passive transport

High Insulin hormone and [Glc] stimulate increased rate of glucose intake

Insulin binds receptor, GLUT4 hexose transporter able to bind cell surface

Hexose Transporters transport glucose into cells in an insulin dependent manner

ExceptionsSmall intestine

Kidney

Which cell typesare affected?

Enzymatic Regulation of GlycolysisEnzymatic Regulation of Glycolysis

CAC intermediates, slow down, there is already adequatesupply of energy

Regulation network samples the condition of the cytoplasm and applies Principles of Supply and Demand

Not moving forward, stop converting ATP

Cellular rxns are converting ATP and ADP, make more ATP

You’ve committed!Bi-phosphated furanoses, keep pathway moving

Glycolysis: Hexokinase IsozymesGlycolysis: Hexokinase Isozymes

Can’t leave the cell with negative charge

I-III IV

Isozymes Different inhibition profiles Location, Km Control point

Hexokinases (I-III)-regulated negatively by Glc-6-P-if later steps slow down, Glc-6P builds up

Glucokinase (IV) in Liver-regulated negatively by Fru-6-P-pulls glucose out of bloodstream until equil-liver can produce more Glc-6-P-converts Glucose to Glycogen storage

Regulation of Phosphofructokinase-1Regulation of Phosphofructokinase-1

Citrate - feedback inhibitor - regulates supply of pyruvate - links Glycolysis and CAC

Fru-2,6-bisphosphate - strong activator - produced by PFK-2 when excess fru-6-phosphate - indirect means of substrate stimulation or feed forward activation

ATP - product of pathway - allosteric inhibitor

AMP - allosteric activator - relieves inhibition by ATP

Large oligomeric enzyme bacteria/mammals - tetramer yeast - octamer

Regulation of Pyruvate KinaseRegulation of Pyruvate Kinase

High blood [Glc]

Allosteric (feed-forward) activation Fructose-1,6-bisphosphate -allosterically activates -produced in step three -links control steps together

+ F 1,6 BP

Inactivation by covalent modification -blood [Glc] drops, glucagon released -liver protein kinase A (PKA) turned on -PKA phosphorylates pyruvate kinase

Allosteric inhibition by ATP -product of pathway and CAC

Low blood [Glc]