Phosphorylates Fructose-6-Pi to Frc-1,6-BisPi:

Catalyzes first committed step of glycolysis, key enzyme to regulate the flux of intermediates through glycolysis.

Regulated allosterically (T-R states)

Negative Inhibitors: ATP, citrate

Positive Effectors: AMP, fructose-2,6-bisphosphate

Carboxylates pyruvate to form oxaloacetate,

ATP required

Biotin cofactor, covalently attached to a lysine residue

Bicarbonate is activated by ATP, it is the source of CO2. Activated CO2 ("carboxyphosphate intermediate") is carried by Biotin to 2nd active site.

Allosterically activated by Acetyl-CoA; must be cound for enzymatic activity. Allows for regulation of cellular energy (gluconeogenesis requires energy; if energy is low pyruvate is directed to TCA)

Pyruvate Carboxylase is found ONLY in matrix of the mitochondria.

Requires AcetylCoA--indicates cellular energy is high enough to carry out gluconeogenesis. If energy requirements are not met, pyruvate is directed into the TCA. AcetylCoA is necessary for the FIRST half of the reaction, the nucleophilic attack of pyruvate on carboxybiotin is not affected by acetylCoA.

Biotin cofactor covalently attached to a Lysine residue.

ATP is a substrate, but concentration is necessary for gluconeogenesis to occur.

Catalyzes the phosphorylation and decarboxylation of oxaloacetate to produce PEP.

The decarboxylation reaction is very exergonic and drives the reaction of PEP synthesis.

**USES GTP FOR ENERGY**

(ATP equivalent)

Can be in the mitochondria or in the cytosol

Can be either in cytosol or mitochondria. If in mitochondria, the oxaloacetate is converted to PEP directly there. PEP is then transported into the cytosol for the remainder of the glycolytic/gluconeogenic enzymes.

If in the cytosol, oxaloacetate must be REDUCED to malate by malate dehydrogenase, so that the malate transporters can carry it out of the mitochondrial matrix and into the cytosol. Then reoxidized to oxaloacetate.

Hydrolyzes fructose-1,6-bp to fructose-6-Pi,

First committed step of gluconeogenesis

Allosterically regulated by:

Negative Effectors: AMP, Fructose-2,6-bisphosphate

Positive Effector: Citrate

Key enzyme for regulating the flux of intermediates through gluconeogenesis

Hydrolyzes the phosphate group off of Glucose-6-Pi to produce glucose.

Membrane bound protein of the LUMEN of the ER in LIVER AND KIDNEYS only.

this is the enzyme that localizes gluconeogenesis to the hepatic tissues.

Regulated by substrate level control (like glucokinase, the glycolytic counterpart in the liver/kidneys), HIGH Km for substrate and thus only dependent on substrate control and only active at high concentrations.

Allosterically regulated:

Negative Effectors: AMP and Fructose-2,6-Bisphosphate

(reverse of PFK I)

Positive Effector: Citrate

Pyruvate Kinase:

PK is reversibly phosphorylated by the cAMP-dependent phosphorylation cascade. Glucagon causes phosphorylation, thus deactivating PK, and turning ON GLUCONEOGENESIS. Insulin causes the hydrolysis of the Pi group, thus activating the PK and turning on glycolysis.

Describes the equillibrium that exists between the muscles and liver in the production and degradation/use of lactate.

Muscles (when vigorously exercising under anaerobic conditions) produce lactate (to regenerate NAD+), lactate is released into the blood stream and carried to the liver.

Liver reoxidizes lactate into pyruvate and converts to glucose via gluconeogenesis. Then releases this glucose into the blood for use by the muscles.

Hexokinase (glucokinase in hepatic tissues)

Phosphofructokinase I

Pyruvate Kinase

All are allosterically regulated so they can be reciprocally regulated by gluconeogenic effectors/enzymes.

Glucose-6-Phosphatase

Fructose-1,6-Bisphosphatase

PEP Carboxykinase and Pyruvate Carboxylase

Allosteric Regulators:

Positive Regulators: AMP, Fructose-1,6-bisphosphate (feed forward)

Negative Effector: ATP, Alanine

cAMP-dependent phosphorylation (direct hormonal control)

storage polysaccaride in animals--glucose linked with a(1-4) glycosidic linkages

found in liver and muscle tissues

liver--to maintain blood glucose levels

muscle--quick energy reserve for muscle action

highly branched structure with many nonreducing ends--branches have a(1-6)glycosidic linkages 

**one reducing end**

Glycogen metabolism is under direct hormonal control:

glucagon, epinephrine, insulin

Necessary for quick mobilization of glucose, many nonreducing ends allow for quick hydrolysis of glucose residues

Branching increases solubility

Lack of "branching enzyme" (can't create a(1-6) branch points) results in long, linear saccharide (like amylose) that alters the shape of liver cells. Causes autoimmune death from Anderson's disease

catalyzes the sequential phosphorolysis of glucose residues from a nonreducing end of a glycogen molecule

releases Glucose-1-Pi from glucagon

oxonium ion intermediate, glycosidic linkage is cleaved by inorganic phosphate in such a way that the stereochemistry at the C1 carbon is maintained (SN1 mechanism)

requires a pyridoxl-5'-phosphate cofactor; covalently bound to a lysine residue via a Schiff base

water is completely excluded from the active site

Allosterically regulated:

Positive Effectors: AMP (low cell energy = need to make ATP so we need glucose for glycolysis) (curve shifts to the LEFT, lower Km, higher affinity, Vmax not affected)

Negative Effectors: ATP, Glucose-6-Pi (curve shifts to the RIGHT, higher Km, Vmax not affected)

ATP = feeback inhibitor (produced along the pathway)

Glucose-6-Pi = Allosteric effector (neg.)

Produce a NEGATIVE effect on the COOPERATIVITY of the enzyme (2 subunits + 2 active sites) (T-R equilib)

**Substrate we're concerned with in the curves is Pi!**

A pyridoxyl-5'-phosphate cofactor is required

it is attached via a SCHIFF BASE (forms an electron sink) to a lysine residue

functions with inorganic phosphate in the gen acid/base catalysis

Removes the branches (glycogen phosphorylase loses activity within 4 residues of a branch point)

TWO ACTIVITIES:

1. a(1,4) transglycosylase (transferase)--move blocks of 3 glucose residues from the branch onto the nonreducing end of the next chain

2. a(1,6)-glucosidase--cleaves the a(1-6) glycosidic linkage at the branch point (releases a GLUCOSE molecule)

90% of the residues mobilized in glycogen metabolism are released as Glucose-1-Pi, but the other 10% are released as Glucose by the glycosidase activity of the debranching enzyme.

Isomerizes Glucose-1-Pi (released by glycogen phosphorylase) to Glucose-6-Pi, which can be utilized by glycolytic enzymes

Requires a PHOSPHORYLATED SERINE residue in the active site (similar to phosphoglycerate mutase)

Intermediate = Glucose-1,6-bisphosphate

Also required in catalytic concentration for phosphorylating the Serine (directly after translation and when intermediate "escapes")

Phosphorylates glucose-1-Pi to glucose-1,6-bisphosphate

binds to a dephosphorylated Serine in phosphoglucomutase (and subsequently phosphorylates it to restore enzymatic activity)

catalyzes the acylation of Glucose-1-Pi with a UTP to create UDP-glucose

(Glc-1-Pi + UTP --> PPi + UDP-Glucose)

UDP glucose "carries" activated glucose molecules

Inorganic Pyrophosphatase is required to make this reaction irriversible, it hydrolyzes the released pyrophosphate molecule into 2Pi

the hydrolysis of released PPi to 2Pi is the thermodynamic determinant of the rxn

catalyzed by inorganic pyrophosphatase

pushes the reaction towards products because it rapidly removes product as soon as it is created

adds new glucosyl residues to nonreducing ends of glycogen, adds residues to a chain of 4 or more residues

SN1 mechanism (retains stereochemistry)

requires a primer protien--glycogenin

UDP glucose is the substrate, UDP leaves (very good LG) in an SN1 mechanism

The remaining oxonium ion is attacked by the nonreducing end of a glycogen molecule, as long as there are open C4 groups, glucoses are continually added

Primer protein for glycogen synthase

contains an oligosaccharide of a(1,4) glucose residues attached to a phenolic oxygen of a TYROSINE residue

glycogenin autocatalytically adds up to seven glucose residues after tyrosine glucosyltransferase attaches a glucose molecule to TYR-195. then glycogen synthase adds the rest of the residues on the open C4 (nonreducing end)

each reducing end of a glycogen molecule is attached to a glycogenin

synthesizes a(1,6) glycosidic linkages (glycogen synthase only synthesizes a(1,4)linkages.

Branching is crucial because it increases the solubility and number of reducing ends of a glycogen molecule. this increases the rate of biosynthesis and degredation.

Enzyme takes a block of ~7 Glc residues and transfers them to an interior site, creating the a(1,6) linkage. The new linkage must be at least 8 residues away from a previous branching point and the 'added onto chain' must be at least 11 residues long.

Anderson's disease--deficiency in branching enzyme. Autoimmune death by age 4.

Glucagon and Epinephrine activate Glycogen phosphorylase by phosphorylating in (via cAMP pathway)

"A" state = PHOSPHORYLATED (locks in the R state)

Phosphorylation is by PHOPHORYLASE KINASE (covalent modification of Ser-14 residue

Dephosphorylation (caused by INSULIN) is done by PHOSPHOPROTEIN PHOSPHATASE 1

Phosphorylase Kinase

(phosphorylates Ser residue--locks into R state (a))

Phosphoprotein phosphatase 1

dephosphorylates the Ser residue, decreasing activity (b-state), insulin sparks this dephosphorylation

Allosterically activated by GLUCOSE-6-Pi --Key allosteric effector

Also reversible phosphorylation:

DEPHOSPHORYLATED = locked in R (a) state, this is the more active state of the synthase

PHOSPHORYLATED = less active, T (b) state of the enzyme, very high Km (phosphorylated by same phosphorylase kinase and other kinases)

Phosphorylase kinase 1 phosphorylates Glycogen synthase.

This DEACTIVATES the enzyme, locking in 'b' or "T" state.

Phosphoprotein phosphatase 1 dephosphorylates glycogen synthase.

This locks enzyme in the active R (a) form.

Glucose-6-Phosphate

Allosteric effector of Glycogen phosphorylase (-)

 and Glycogen synthase (+)