Lecture 16: Carbohydrate Metabolism Flashcards
Gluconeogensis
provides gluccose
reciprocal regulation
Cori Cycle
reciprocal regulation
different directions
Glycolysis regulated by PFK1
Gluconeogenesis regulated by f16BPase
all controlled by allosteric regulator F2-6BP, energy charge, and citrate levles
Cori Cycle overview
recycle lactate
export lactate to liver
convert it to pyruvate
synth glucose by gluconeogenesis
What does gluconeogensis accomplish?
liver and kidney cells
make glucose from non carbo sources like glycerol, a.a.s lactate, etc
plants use it to make GAP glucose
how many ATP needed for glucconeogenesis
4 ATP
2 GTP
2 NADH
SIX ATP
key enzymes?
pyruvate carboxylase: convert pyruvate to OAA (ALSO IN CITRATE CYCLE)
responsible for just gluconeo
PEPCK: OAA to PEP
FBPase-1 (1,6 BPase) catalyze dephosphylation of fructose to make fructose 6P
Glucose 6PL catalyzes dephosphory of G6P to make glucose
Glycolysis and gluconeogensis…
OPPOSING PATHWAYS
so substrate concs dictate what direction reactions run
EXCEPT for specific pathways that use specific enzymes
examples of bypass enzymes in gluconeogenesis that reverse the glycolysis reaction
Fructose 1,6 BPase
G6P
Net ATP from glycolysis
2
What if we ran glycolysis and gluconeogensis at the same time ??
We would use 4 ATP if we ran glycolysis and gluconeogensis at the same time
(you get 2 from glycolysis, but we burn through 6 in gluconeogenesis, meaning we burn through 4 ATP total if run at same time)
SO why is it important that pathways are regulated?
don’t want to waste ATP!
So don’t want to run glycolysis and gluconeogensis at the same time
Glycolytic and gluconeogenic pathways are very regulated. How?
Energy charge, acetyl CoA, citrate, alanine are metabolites
F-2, 6 BP is reciprocal regulator
all act on opposing enzymes in pathways
Glycolysis inhibitors
ATP
citrate
Glycolysis stimulators
F-2,6 BP
AMP
Gluconeogenesis inhibitors
F-2,6 BP
AMP
Gluconeogenesis stimulators
citrate
pyruvate kinase inhibitors
(regulates glycolysis) (takes pyruvate to OAA)
ATP
Alanine
pyruvate kinase stimulators
(regulates glycolysis)
F-2,6 BP
PEPCK inhibitors
ADP (regulates Gluconeogenesis)
Pyruvate carboxylase inhibitors
(regulates Gluconeogenesis)
ADP
Pyruvate carboxylase stimulators
(regulates Gluconeogenesis)
Acetyl CoA
Why do we consider the reactions regulated by Pyruvate carboxylase and PEPCK a cost of 4 ATP to convert pyruvate to PEP when we count up the # of ATP needed to generate 1 glucose from 2 pyruvate
We have to run the pair of reactions twice!
if we are making glucose, we need SIX carbons, that means we need TWO pyruvates. Each time, this takes 2 ATP (total of 4)
why do we count GTP as an ATP
because there is no free nrg change to interconvert ATP and GTP
pyruvate carboxylase
pyruvate to OAA, its modified to do this rxn
lysine residue
long swinging arm between the two active sites of the enzyme
where have we seen this enzymatic reaction before? (its activated by acetyl CoA and generates OAA)
citrate cycle!!!!
its activated by acetyl CoA
where is this all taking place???
pyruvate to OAA happens in matrix
all of the rest of glycolysis and gluconeogenesis happens in the cytosol
so how does OAA get to cytosol?
OAA is converted to malate to leave the matrix and go to the cytosol
NADH NEEDED
malate goes back to OAA once it gets to matrix
glyceraldehyde 3P dehydrogenase
NADH is given to it in glycolysis
OPPOSITE OF when there is NAD+ in the cytosol and NADH needs to be regernated during GLYCOLYSIS
Reciprocal regulation definition
levels of metabolites inhibit one enzyme and stimulate another
F-2BP
NOT a metabolite
JUST A REGULATOR of PFK1 and PBPase-1
substrate is glucose 6- phoshpate
What is the metabolic logic of reciprocal regulation by citrate?
lots of citrate that we don’t need to make more nrg
so we start making glucose instead
turn on and off 2 pathways with same metabolite=no waste of nrg
Does high F-2,6 BP activate or inhibit flux through the glycolytic pathway
activates
Presence of F-2,6BP and PFK-1
when it is present, it takes a lot less activity to reach half max activity
when absent, it takes a lot more substrate to reach half max
25X times higher affinity of PFK1 for its substrate when F-2,6 BP is present
Presence of F-2,6BP and FBPase-1
substrate of FBP-ase 1 is fructose bisphosphate
when F-2,6BP present, it takes more enzume to make half max activity: substate affinity is 15X lower
Does low F-2,6 BP activate or inhibit flux through the gluconeogenic pathway?
ACTIVATES
how is amount of F-2,6BP controlled?
by dual function enzyme PFK-2/FBase-2
it has TWO active sites
Is PFK-2/FBase-2 one protein with 2 catalytic activities, or two proein subunits that form one quatenary complex
one protein with 2 catalytic actibities
its one polypep chain
center part connects them
the activity of one domain INHIBITS the activity of the other
Glucagon signaling and PFK-2/FBase-2
stimulates phosphorylation of the enzyme (Through protein kinase a–PKA)
ACTIVATION of FBP-ase 2 domain
Insulin signaling of PFK-2/FBase-2
stimulates dephosphorylation of enzyme
ACTIVATION of PFK-2 domain
low blood sugar
glucagon signals
activate protein kinase a
phosphorylates one of PFK-2/FBase-2 domains: inactivates PFK-2 domain
FBP-ase 2 activated
fructose 6 phospate made from fructose bisposphate
more active gluconeogenesis
high blood sugar
insulin signals activate protein phosphatase one actviates PFK-2 domain (dephosphorylate the domains) catalyze to make fructose bisphosphate more active glycolysis
low blood sugar… whats active/not
glycolysus LESS active
gluconeogenesis MORE active
high blood sugar…whats active/not
glycolysis MORE active
gluconeogenesis LESS active
so what does level of F-2,6 BP do?
recipricoally regulate the enzymes
lots of one activates one pathway
lost of other activates other pathway
inhibits whats not active
phosphorylating glucose with hexokinase does what
traps glucose in the cell
but what about glucose 6P?
it can be imported into the ER and is dephosphorylayed
levels lumen
goes out of cell for use elsewhere
Cori cycle
what happens to lactate made by anerobic muscle ativity lactate goes to liver (gluconeogenesis) liver converts it back to pyruvate NADH produced (can be used by GAP) pyruvate can go back to glucose
so whats the point of the cori cycle??
a way we can keep doing glycolysis to get nrg from muscle cells
seperate locations for these pathways. happen in different tissues
Cori cycle cost
4 ATP
Explain why the Cori cycle has a net cost of 4 ATP to the organism?
we produce 2 ATP in skeletal muscle
costs 6 ATP in the liver
so why do we do the Cori cycle if it costs 4 ATP?
if muscles need nrg, you have to get it somehow
why do altheletes warm down?
enhances circulation
lactate can be cleared from muscles and used in liver for glucose synth via cori cycle
