Part 3.2 Flashcards
Insulin binding receptor response pathway
1) Insulin binds alpha subunits of receptor
2) Conformational change in transmembrane domain of beta subunit which results in autophosphorylation of tyrosine residues (RTK activity)
3) receptor serves as hub recruiting proteins to it like IRS-1
4) IRS-1 (insulin response substrate) signals 2 cascades: PI3K and GRB-2
5) PI3K –> PKB –> altered protein/enzyme activity like ↑ GLUT4 to membrane and GS activity
GRB2 –> Ras –> altered gene transcription like ↑ glucokinase transcription
Pathway insulin activates glycogenesis and inactivates glycogenolysis
Activation of glycogenesis:
1) IRS-1/PI3K/PKB (protein kinase B) activates PP1 and inhibits GSK3 via phosphorylation
2) PP1 dephosphorylates glycogen synthase (and G6P allosterically activates)
Inhibition of glycogenolysis:
1) PKB activates PP1
2) PP1 inhibits phosphorylase kinase (PK) and glycogen phosphorylase
- also allosterically inhibited by G6P, glucose and ATP
Role of F-2,6-BP
Regulation of F-2,6-BP
Role: signaling molecule which activates PFK-1 to increase glycolysis (↓ F-2,6-BP stimulates FBPase-1)
- PFK-2/FBPase-2 is a single bifunctional enzyme
Regulation:
1) Insulin stimulates PFK-2 activity to produce more F-2,6BP production from fructose-6-phosphate
2) Glucagon stimulates FBPase-2 activity to ↓ [F-2,6BP] and ↑ [F6P]
Effect of F-2,6-BP on Vmax of PFK-1 and FBPase-1
PFK-1 Vmax: Addition of F-2,6-BP helps PFK-1 to reach Vmax with a smaller [fructose-6-phosphate]
FBPase-1 Vmax: Removal of F-2,6-BP helps FBPase-1 to reach Vmax with smaller [fructose-1,6-phosphate]
Insulin vs. glucagon regulation pathway of PFK-2/FBPase-2 activity
1) Glucagon –> PKA
2) PKA phosphorylates PFK-2 part inactivating it
- ↓ F-2,6-BP
- ↑ gluconeogenesis
1) Insulin –> PKB—->PP1
2) PP1 dephosphorylates PFK-2 part activating it
- ↑ F-2,6-BP
- ↑ glycolysis
PKB’s main actions
PP1 main actions
Insulin pathway
PKB: phosphorylates PP1 (active) and phosphorylates GSK3 (inactive)
PP1 dephosphorylates PFK-2 component (active)
PP1 desphosphorylates glycogen phosphorylase and phosphorylase kinase (inactive)
PP1 dephosphorylates ACC (active) to stimulate lipogenesis
Broad strokes how insulin increases glycolysis and lipogenesis in adipocytes
1) Insulin increases glucose uptake into the cell, which increases glycolysis.
2) Glycolysis metabolites stimulate ChREBP binding to ChoRE
3) Insulin activates SREBP-1c movement into the nucleus and binding SRE
4) Together target genes involved in lipogenesis are transcribed, increasing de novo lipogenesis
5) the pathways all converge to produce pyruvate, acetyl-coA and citrate
Citrate shuttle to FA synthesis
1) Under fed conditions as Krebs cycle flux slows down, citrate accumulates in mitochondria
2) Citrate exits via citrate transporter to cytosol
3) ATP-Citrate lyase catalyzes citrate –> oxaloacetate + acetyl CoA
4) Acetyl coA + CO2 + ATP –> malonyl coA (x7) catalyzed by ACC
5) 7 Malonyl coA + Acetyl CoA + 14 NADPH –> 1 palmitate catalyzed by Fatty Acid Synthase
6) Oxaloacetate + NADH –> malate by malate dehydrogenase
7) Malate NADP+ –> pyruvate + NADPH by malic enzyme for pyruvate re-entry into mitochondria via pyruvate transporter
8) Pyruvate + CO2 + ATP –> oxaloacetate by pyruvate carboxylase
- biotin dependent reaction
ACC about
Acetyl coA Carboxylase
Rate limiting step of FA synthesis
Biotin dependent
1) Insulin signaled PP1 dephosphorylates ACC activating it
2) ACC is more active when polymerized
- ↑ [citrate] promotes polymerization and is an allosteric activator
Adenylate kinase
Adenylate kinase catalyzes 2 ADP –> ATP + AMP
How AMPK functions as the body’s fuel gauge
1) As ATP is used, ADP is formed
2) ADP –> ATP + AMP by adenylate kinase
3) ↑ [AMP] activates AMPK
4) AMPK activates ATP producing pathways and inactivates ATP consuming pathways
ex. AMPK phosphorylates ACC to prevent lipogenesis
ChREBP activates which lipogenesis genes?
Genes encoting ATP-citrate lyase, ACC, FA synthase and desaturase
