Glycolysis and gluconeogenisis regulation Flashcards
Irreversible steps
regulation of glycolysis and gluconeogenisis is to prevent futile cycling
Glucose—-Glucose 6 phosphate (>hexokinase, PFK1, oxaloacetate (pyruvate carboxylase)
oxaloacetate–>PEP (PEPCK)
Types of regulation
Allosteric: regulation by substrates, products, cofactors
Covalent modification: (de)phosphorylation that changes enzymatic activity
genetic control (GLUT4 and hexokinase)
cell localization: PEPCK in cyto and pyruvate carbaoxylase in mito
Regulation of glycolysis (hexokinase)
hexokinase is inhibited by feedback inhibition of G6P
normal glycolysis doesnt make enough G6P to inhibit hexokinase
If PFK1 is turned off, G6P will be in high enough concentrations that it will inhibit hexokinase
Glucokinase is not inhibited by G6P but is regulated by a high Km
Regulation of glycolysis PFK1
PFK1 is the rate limiting step of glycolysis
Regulated at muliple levels
Activators of PFK1
Fructose 6 phosphate
Fructose 2 6 bisphosphate
AMP, ADP
Inhibitors of PFK1
ATP (interferes with AMP activation)
Phosphorylation (decreases substrate affinity)-only in liver
Citrate- allosteric
Allosteric regulation of PFK1
2 state model: R state (active), relaxed state- activators bind T state (inactive), taut state- inhibitors bind
ATP concentration is a signal for energy content of cell
ATP is a feedback inhibitor of PFK1, and a substrate
ATP alters the Km for the substrate Fructose 6 phosphate
AMP, ADP, Pi- allosteric activator and compete for binding site
Citrate/pH control of PFK1
citrate is an intermediate in the TCA and a feedback inhibitor of PFK1 in the same way as ATP
it lowers the pH
glucose being used and lactic acid (low pH) stops glycolysis through PFK1
Fructose 2 6 bisphosphate
increases the rate of PFK1 in liver
controls carbon flux in glycolysis and gluconeogenisis
its a regulator not an intermediate that sets rate
its hormonally regulated by insulin and glucagon
it modifies the Km of PFK1
reduces ATP and increases Fructose 6 phosphate by decreasing the Km and increasing the Vmax
PFK 2
PFK2: fructose 26 bisphosphate -> fructose 6 phosphate
fructose bisphosphatase 2: Fructose 6 p-> fructose 26 bisphosphate
bifunctional enzyme thru (de)phosphorylation via protein kinase A
if its phosphorylated its fructose bisphosphatase 2
it its dephosphorylated its PFK2
Fasting vs fed state
fasted state:
high glucagon-> high cAMP -> high protein kinase A-> fructose bisphosphatase 2
(less glycolysis, more gluconeogenisis)
Fed state:
high insulin -> low cAMP -> low protein kinase A -> PFK2
(more glycolysis, less gluconeogenisis)
Pyruvate kinase regulation
PEP–> pyruvate and ATP
Allosteric activators:
- fructose 1 6 disphosphate
- PEP
Allosteric inhibitors:
- ATP
- alanine
- Phosphorylation (via protein kinase a )
Oxygen and pyruvate
(pyruvate and NADH)–> lactate and NAD+
via lactate dehydrogenase
Anaerobic glycolysis: NAD+ is regenerated with production of lactate
Aerobic glycolysis: NAD+ is regenerated by shuttling the reducing equivalents into the mito (oxidative phosphorylation)
NAD+ regeneration during aerobic glycolysis
2 shuttles (glycerol 3 phosphate dehydrogenase and malate)
glycerol 3 phosphate dehydrogenase shuttle:
cytosolic DHAP+ NADH–> gycerol 3 phosphate +NAD+ (thru glycerol 3 phosphate dehydrogenase)
outer mito glycerol 3 phosphate dehydrogenase takes the NAD and converts it to FAD and FADH2 in ETC
Malate aspartate shuttle
Cyto oxaloacetate and NADH–> malate and NAD+ (via malate dehydrogenase)
then transporter takes malate by producing NADH and pumps out oxaloacetate
additional substrates for glycolysis
Fructose: enters glycolysis 2 ways that are tissue specific
direct phosphorylation via hexokinase to make fructose 6 phosphate (its slow compared to glucokinase)
in liver [glucose] is way higher [fructose], so you need another way:
Fructokinase (makes F6P) using ATP -> fructose 1 p aldolase B (makes DHAP and glyceraldyhyde)
DHAP->-> GA3p-> glycolysis (through triosephosphate isomerase)
glyceraldyhde->GA3P > glycolysis (throu triose kinase and ATP)
Galactose-> Galactose 1 p (via galactokinase and ATP)–> glucose 6 p->glycolysis (via uridyl transferase, UDP 4 epimerase)
Inherited defects of glycolysis and transcriptional control
very rare pyruvate kinases are most of them
transcriptional control
gluconeogenisis -> upregulates PEPCK via FOX
glycolysis-> down regulates PEPCK
Cori cycle
Under anaerobic conditions, pyruvate formation exceeds oxidation rate from TCA, the rate of NADH formation from glycolysis is greater than oxidation from ETC
to continue glycolysis, active skeletal muscle depends on NAD+ for the oxidation of glycerol 3 phosphate so it sends its lactate to the liver
Pyruvate + NADH -> Lactate + NAD+
Lactate is converted to pyruvate-> glucose to muscle
