Week 4A: Integration Metabolism, Role of Organs, Feast/Famine, Diabetes Mellitus & Alcohol Flashcards
HC23-26
Kinetics curve of multidomain enzymes with regulatory and catalytic domains
Sigmoidal curve
> sum curve R-state and T-state.
> do not obey Michaelis Menten kinetics
Multidomain, regulated enzymes are usually the ..
catalysers of the committed step in a pathway.
is HMG-reductase a monomer?
No, a highly regulated dimer: committed step in cholesterol biosynthesis
Which enzyme is targeted by statins?
HMG-CoA reductase
> also upregulates LDLR: higher dose used in homozygous FH than heterozygous FH (familial hypercholesterolemia)
Phosphorylation regulation in glycogen metabolism
Glycogen phosphorylase (GP): breakdown and glycogen synthase (GS): synthesis.
> a-forms, normally in active R-state
> allosteric metabolites can overrule phosphorylation status
> phosphorylation of GP and GS via PKA for example
> activates GP, inactivates GS
Phosphorylation regulation in fatty acid metabolism (acetyl-CoA carboxylase in synthesis)
Active carboxylase when dephosphorylated by PP2A.
Inactive carboxylase when phosphorylated by AMPK (AMP-activated protein kinase)
Difference AMPK and adenylate kinase
AMPK uses AMP and ATP to phosphorylate a protein
> result, AMP still bound, ATP to ADP for phosphorylation.
Adenylate kinase: ADP + ADP <=> ATP + AMP for extra energy
Why is the regulation of acetyl-CoA carboxylase logic?
When high AMP, low energy, no FA synthesis wanted.
AMPK phosphorylates and inactivates ACC
Metabolite regulation of liver and muscle glycogen phosphorylase
Liver: glucose can allosterically bind and inactivate the GP-a for change to T-state (even when phosphorylated in a form)
Muscle: binding AMP to get in R state as GP-b
Binding ATP or G-6-P causes change to T-state. (enough energy, no breakdown glycogen needed)
> not necessarily in a or b form, but it shows the overruling of phosphorylation state
Why isn’t liver GP inactivated by AMP?
The liver is the glucose homeostasis regulator and can convert G-6-P to glucose with G6Pase and needs to consider other tissues needs, not only its own
Metabolites may overrule phosphorylation regulation of enzymes: Acetyl-CoA carboxylase
Phosphorylated ACC is inactive. But if it binds citrate (shows that there is enough energy, TCA cycle stopped), than partly active ACC. (FA synthesis committed step)
Which enzymes is regulated as regulatory filaments?
Acetyl-CoA carboxylase forms regulatory filaments
> Palmitoyl-CoA (intermediate FA oxidation/breakdown) causes filaments to disassemble (product inhibition) to inactive dimers > induces conformational changes as a regulator
Name catabolic pathways and anabolic pathways (interconnected)
Catabolic:
- oxidation
- oxidative decarboxylation
- oxidative deamination
Anabolic
- Reductive biosynthesis
- Carboxylation
- Synthesis
Control of metabolic fluxes
-Based on energy states: fed, fasted, starvation
-Irreversible steps set the pace
Manipulation of metabolic fluxes
-Changing enzyme activities at irreversible steps with the high flux control (short term)
-Changing multiple activities at the same time: controlled gene expression (long term)
An irreversible step is a reaction with a large .. value
Keq
= [C][D]/[A][B]
in A + B <=> C + D
And large negative dG0
> change flux by changing enzyme activity or amount of enzyme
Reversible step has a … dG0 and flux can be changed by …
small, flux changed by changing concentrations of reactants
ATP yield of 1 glucose
Glycolysis: 2 ATP and 2 NADH (22.5=5)= 7 ATP
-Pyruvate oxidation: 2 NADH = 5 ATP
-TCA cycle: 2 acetyl CoA yields 2 times 3 NADH + 1 FADH2 + 1 GTP so 2 (7.5 ATP [3+2.5] + 1.5 [FADH2] + 1 [GTP] = 20 ATP
> total 30-32 ATP
1 glucose yields 30-32 ATP, dependent on
Shuttle which is used (redox) across mitochondria for NADH of glycolysis
- Glycerol-3-phosphate
- Malate-aspartate
Glycerol-3-phosphate shuttle
shuttle in muscle: DHAP in cytosol converted to glycerol-3-P by cytoplasmic glycerol-3-P dehydrogenase (GAPDH, using NADH) in intermembrane space and glycerol-3-P and this is converted by mitochondrial GAPDH to DHAP (yielding FADH2).
> 2 cytosolic NADH and yields 2 mitochondrial FADH2: 1.5 ATP per FADH2: 3 ATP. 30 ATP total
> turbo glycolysis
Malate-acetate shuttle
shuttle in liver, brain and heart muscle: 32 ATP yield. NADH reduces oxaloacetate in cytosol to malate and transport to matrix and in matrix conversion malate to oxaloacetate and through a-ketoglutarate and aspartate (converted from glutamate, coupled to oxaloacetate> a-ketoglutarate) back to cytosol. In cytosol conversion a-ketoglutarate to oxaloacetate (oxidize NADH) and aspartate to glutamate (tranport to matrix)
> 2 cytosolic NADH to 2 NADH in matrix: 2.5 ATP per, total 5, total 32 ATP
What happens to the FADH2 from glycerol-3-phosphate shuttle
Flavoprotein which donates electrons to coenzyme Q in ubiquinone (Q) form (reduced to ubiquinol QH2).
What happens to beta-oxidation created FADH2?
Electron-transfer protein (ETF) with the FADH2 prosthetic group.
> gives to Q
malate-aspartate shuttle is slower than glycerol-3-phosphate shuttle?
More enzymes involved.