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Y Biochemistry 2 > Midterm II: Fatty Acid Oxidation (Ben) > Flashcards

Midterm II: Fatty Acid Oxidation (Ben) Flashcards

1
Q

What are longer free fatty acids bound to for transport in the blood?

How many FAs per unit of this transport molecule?

A

Albumin

  • 10 FAs per albumin monomer
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2
Q

How does transport of shorter chain fatty acids differ from longer?

A

SCFAs are more water-soluble and exist in unionized or anion forms

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3
Q

What is the first step of catabolism of a free fatty acid?

What is special about this step energetically?

A

Fatty Acid Activation

  • with CoA and ATP via acyl-CoA synthetase
  • it is the ONLY step of FA oxidation which uses ATP
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4
Q

What is the enzyme which “activates” fatty acids for oxidation and where is it found (4 locations)?

A

Acyl-CoA Synthetase

Found:

  1. in the ER
  2. in peroxisomes
  3. in mitochondria
  4. on mitochondrial outer membrane
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5
Q

What is the overal reaction of FFA activation?

Include the enzyme.

A

FFA + CoA + ATP

—- acyl-CoA synthetase —->

acyl-CoA + PPi + AMP

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6
Q

What happens to the PPi formed from cleaved ATP during fatty acid activation and why?

A

it is hydrolyzed by inorganic pyrophosphatase

  • to ensure that the reaction is carried out fully and is irreversible in vivo
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7
Q

What is the site of fatty acid activation?

A

the outer mitochondrial membrane

(where acyl-CoA synthetase is found)

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8
Q

What happens to acyl-CoA in the intermembrane space?

(before it can enter the mitochondrial matrix)

A

Carnitine Palmitoyltransferase-I

(or Carnitine Acyltransferase-I)

  • catalyzes transfer of acyl group from CoA to carnitine to form acylcarnitine
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9
Q

How does acylcarnitine penetrate the inner mitochondrial membrane?

A

via Carnitine-Acylcarnitine Translocase

  • exchanges carnitine for acylcarnitine across the membrane
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10
Q

What happens to acylcarnitine once it is inside the mitochondrial matrix?

Start with the enzyme, then describe the process.

A

Carnitine Palmitoyltransferase-II

(or Carnitine Acyltransferase-II)

  • transfers acyl group to CoA reforming Acyl-CoA and liberating carnitine
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11
Q

Where is Carnitine Palmitoyltransferase-I located?

A

across the outer mitochondrial membrane

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12
Q

Where is Carnitine-AcylCarnitine Translocase located?

A

across the inner mitochondrial membrane

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13
Q

Where is Carnitine Palmitoyltransferase-II located?

A

on the inside of the inner mitochondrial membrane

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14
Q

Why is β-oxidation called β-oxidation?

A

because it is a cycle of successive cleavages of Acyl-CoA molecules at…

the C-C bond between the α(2) and β(3) carbons

(2nd and 3rd Cs from the -COOH end)

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15
Q

What is the collective name for the enzymes which perform β-oxidation?

And where are they found?

A

Fatty Acid Oxidase

  • found in the mitochondrial matrix and inner mitochondrial membrane

(adjacent to to the respiratory chain)

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16
Q

Energetically, what are the important products (3) of β-oxidation?

How are they used?

A
  1. FADH2 - oxidative phosphorylation > ATP
  2. NADH - oxidative phosphorylation > ATP
  3. Acetyl-CoA - citric acid cycle > ATP + NADH + FADH2
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17
Q

What is the first step of β-oxidation?

Substrates/reactants?

Enzyme?

Products?

A

Removal of one hydrogen each from α and β carbons…

Reactants: Acyl-CoA + FAD

Enzyme: Acyl-CoA Dehydrogenase

Products: Δ2-trans-Enoyl-CoA + FADH2

18
Q

What is the 2nd step of β-oxidation?

Substrates/reactants?

Enzyme?

Products?

A

Water is added to saturate the double bond…

Reactants: Δ2-trans-Enoyl-CoA + H2O

Enzyme: Δ2-Enoyl-CoA Hydratase

Products: L-β-Hydroxy-acyl-CoA

19
Q

What is the 3rd step of β-oxidation?

Substrates/reactants?

Enzyme?

Products?

What is special about the enzyme?

A

Further dehydrogenation of the 3-carbon…

Reactants: L-β-Hydroxyacyl-CoA + NAD+

Enzyme: β-Hydroxacyl-CoA Dehydrogenase

Product: β-Ketoacyl-CoA + NADH + H+

The enzyme is stereospecific for the L-isomer.

20
Q

What is the 4th step of β-oxidation?

Substrates/reactants?

Enzyme (2 names)?

Products?

How is one of the end products different from what entered β-oxidation?

A

Cleavage at the 2,3 position…

Reactants: β-Ketoacyl-CoA + CoA-SH

Enzyme: Thiolase (or Acyl-CoA Acetyltransferase)

Products: Acetyl-CoA + Acyl-CoA

Acyl-CoA product here is 2 carbons shorter than acyl-CoA which entered the cycle.

21
Q

How does a fatty acid chain’s length affect how it is transported into the mitochondria?

A
  • > 12C - with carnitine
  • < 12 C - without carnitine, activated in mitoch.
22
Q

Which β-oxidation enzyme has 3 different isoforms?

What for?

What are they?

Which one is frequently deficient?

A

Acyl-CoA Dehydrogenase (the 1st step)

  • for different lengths of fatty acids
  • LCFAs (C 12-18)
  • MCFAs (C 4-14) - frequently deficient (MCAD)
  • SCFAs (C 4-8)
23
Q

How many ATP are ultimately formed per NADH produced in β-oxidation?

Per FADH2?

A

NADH - 2.5 ATP

FADH2 - 1.5 ATP

24
Q

Where are > 12 C FAs oxidized?

And < 12 C?

A

> 12 C - on the inner mitochondrial membrane

< 12 C - via soluble enzymes in the mitochondrial matrix

25
Q

What is special about the last 3 enzymes of β-oxidation?

And what are the 3 enzymes?

A

they are a tightly associated trifunctional protein

  • enoyl-CoA hydratase
  • β-hydroxyacyl-CoA dehydrogenase
  • thiolase
26
Q

What results from the breakdown of an odd-chain fatty acid?

Where can this go and what can it become?

A

The remaining 3C residue is…

Propionyl-CoA

…which is converted to succinyl-CoA and enters the citric acid cycle

  • in this way, it is the only glucogenic part of any fatty acid
27
Q

How are very long chain fatty acids oxidized?

What products result from this?

A

VLCFAs (C20/22) are oxidized in peroxisomes

  • forming acetyl-CoA** and **H2O2
  • BUT this β-oxidation sequence ends at Octanoyl-CoA and is continued in mitochondria
28
Q

What is the first step of glycerol conversion to a glycolysis intermediate in the liver?

Enzyme + product + special reactant

A

Phosphorylation of glycerol…

Reactants: Glycerol + ATP

Enzyme: Glycerol Kinase

Products: Glycerol-3-phosphate + ADP

29
Q

What is the 2nd step of glycerol conversion to a glycolysis intermediate in the liver?

(Enzyme + products + special reactants)

A

Dehydrogenation of G-3-P…

Reactants: G-3-P + NAD+

Enzyme: Glycerol-3-phosphate Dehydrogenase

Products: DHAP + NADH + H+

30
Q

What two hormones induce increased fatty acid oxidation in the fasting/low-glucose state?

How?

A

Epinephrine/Adrenaline + Glucagon

Induce increased oxidation via:

  • Phosphorylation/Inhibition of Perilipin (lipid droplet “protecting” protein)
  • Activation of Hormone-sensitive Lipase
31
Q

High levels of what 3 molecules inhibit fatty acid oxidation?

(think products of oxidation + substrates for FA synthesis…)

A
  1. Malonyl-CoA
  2. NADH
  3. Acetyl-CoA
32
Q

What effect does Malonyl-CoA have on fatty acid oxidation?

How?

A

it inhibits it via…

inhibition of Carnitine Acyltransferase I

which keeps fatty acids from entering the mitochondria

33
Q

What effect does increased NADH have on fatty acid oxidation?

How?

A

it inhibits it via…

inhibition of 3-hydroxyacyl-CoA Dehydrogenase…

the 3rd enzyme in beta-oxidation

(which it is a product of… so simple allosteric inhibition)

34
Q

What effect does increased Acetyl-CoA have on fatty acid oxidation?

How?

A

it inhibits it via…

inhibition of thiolase…

(the last enzyme of beta-oxidation)

which it is a product of… so simple allosteric inhibition

35
Q

What is an important mechanism for long-term upregulation of fatty acid oxidation?

Levels of what general group of metabolic molecules are increased by this mechanism?

A

PPAR-α

(Peroxisome Proliferator-Activated Receptor α)

  • a nuclear receptor protein
  • increases transcription of fatty acid oxidation enzymes
36
Q

What are some endogenous and exogenous ligands of the PPAR system?

A

endogenous: fatty acids (arachidonic + other PUFAs)
exogenous: fibrates (drug class for dyslipidemia)

37
Q

In what tissues is PPARα found?

And what genes does it upregulate transcription of?

and downregulate?

A

Liver, Muscle, Adipose Tissue

Upregulates:

  • Fatty Acid Transporters
  • Peroxisomal FA Oxidation Enzymes
  • CAT I + II
  • Lipoprotein Lipase
  • Apo A1/2
  • Acyl-CoA Synthase + Dehydrogenase

Downregulates: Apo CIII

38
Q

What is the most common genetic defect of fatty acid oxidation?

A

Acyl-CoA Dehydrogenase deficiency

  • specifically the medium-chain isoform
39
Q

What are the symptoms of Acyl-CoA dehydrogenase deficiency?

And treatment?

A

Symptoms:

  • Hypoglycemia
  • Decreased ketogenesis
  • Hepatic lipid accumulation
  • Vomiting + drowsiness

Treatment:

  • Frequent carbohydrate-rich meals
  • Carnitine supplementation
40
Q

What 3 enzymes break down triglycerides after perilipin deactivation?

A
  1. Adipocyte Triglyceride Lipase (ATGL) - TG —> DG + FA
  2. Hormone Sensitive Lipase (HSL) - DG —> MG + FA
  3. Monoacylglycerol Lipase (MGL) - MG —> FA + Glycerol

Y Biochemistry 2 (24 decks)

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