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Biochemistry Cardio > Beta-Oxidation > Flashcards

Beta-Oxidation Flashcards

1
Q

Location of beta-oxidation

What are the exception?

A

Mitochondria

Exceptions = RBC and brain

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2
Q

Hormones that stimulate B-ox

A

Glucagon, Epi

Fasting state

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3
Q

What does each round produce?

A

1 NADH

1 FADH2

1 Acetyl-CoA (which can be further oxidized for energy production)

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4
Q

Fatty Acid Activation

A

Mobilized FAs (from adipocytes) enter the cytosol…

There they are activated by Coenzyme A (CoA) … before they are transferred into the mitochondria

  1. FA —> Fatty acyl-adenylate intermediate and PPi (Fatty acyl CoA synthetase)…enzyme still bound to substrate
  2. PPi is immediately hydrolyzed to 2Pi (neg. delta G)…and FA-adenylate is activated with CoA (Fatty Acyl-CoA)
    AMP is also released
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5
Q

Three pathways that the FA-CoA synthetase is used in…

A
  1. TG formation
  2. Glycerophospholipid formation
  3. Prelude to transport of FA into mitochondria (Beta-Ox)
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6
Q

FA-carnitine shuttle

A

Transfer system to get FA-CoA from cytosol to matrix of mitochondria

  1. Carnitine acyl-transferase I (CAT1) —> transfers FA-CoA to carnitine in cytosol (CoA is recycled)
  2. FA-carnitine is transported through outer membrane than through a transporter in the inner mito membrane
  3. Once in the matrix…CATII converts FA-carnitine back to FA-CoA
  4. Carnitine is shuttled back to the cytosol to be reused

**once in the matrix…committed to the beta-ox reaction

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7
Q

Carnitine deficiency

A

Can be produced in liver and kidney…but most comes from diet

Cannot used long chain FAs for energy production

Primary = autosomal recessive…CAT1 (liver) or CAT2 (cardiac and skeletal muscle) is dysfunctional

Secondary = liver disease, malnutrition…

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8
Q

The four repeating reactions of beta-ox

General

A
  1. Oxidation
  2. Hydration
  3. Oxidation
  4. Cleavage
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9
Q

1st oxidation step of Beta-ox

A

Enzyme: acyl-CoA dehydrogenase

Energy production: FADH2

Fatty acyl-CoA is oxidized and a double bond is formed between the alpha and beta carbons (trans configuration)

Product: trans-delta2-enoyl-CoA

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10
Q

Hydration step if beta-ox

A

Enzyme: Enoyl-CoA hydratase

Adds H2O across the double bond that was formed between the alpha and beta carbons

Product = beta-hydroxylacyl-CoA

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11
Q

2nd oxidation reaction of beta-ox (3rd overall reaction)

A

Enzyme: beta-hydroxyacyl-CoA dehydrogenase

Energy production: NADH + H

Oxidizes at the beta carbon to make…
Beta-ketoacyl-CoA (ketone group on beta carbon now (C=O)

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12
Q

Cleavage reaction in beta-ox

A

Enzyme: acyl-CoA acetyltransferase (thiolase)

2C unit (carboxyl and alpha carbons) is cleaved away as Acetyl-CoA…

The second CoA is attached to the beta-carbon which now becomes the new carboxyl (C1) to subsequent reactions —> repeat step #1

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13
Q

How many times can palmitate undergo beta-ox?

C16:0?

A

6 repeated steps = 6(FADH2 + NADH + Acetyl-CoA) + 4C Fatty acyl-CoA

7th reaction = FADH2 + NADH + 2Acetyl-CoA

Final Yield: 7(FADH2 + NADH) + 8 Acetyl-CoA

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14
Q

Fate of NADH/FADH2 and Acetyl-CoA

A

NADH/FADH2 = e-transport chain

Acetyl-CoA = citric acid cycle

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15
Q

Acetyl-CoA = # ATP?

A

10

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16
Q

NADH = #ATP

A

2.5

17
Q

FADH2 = #ATP?

A

1.5 ATP

18
Q

Medium chain acyl-CoA dehydrogenase deficiency (MCADD)

A

One of the most common inborn metabolic errors

AR

Deficiency in the Acyl-CoA dehydrogenase (first step enzyme in B-ox)

Has a higher affinity for medium chain FAs…so reduced ability to oxidized 6-10 length

Symptoms: accumulation of 6-10 FAs, low blood glucose, muscle weakness, sleepiness, vomitting, coma

Diagnosis = by high 6-10 and dicarboxylic acids in the urine

Cause of sudden infant death syndrome (SIDS)

Part of core panel of disorders screened for

Treatment = low fat/high carb diets…important to avoid fasting

19
Q

Omega-FA oxidation

A

Minor route for MCFA oxidation

Carboxylic acid is produced on omega end —> dicarboxylic acid produced

These can enter the mito and oxidized by normal beta-ox

Ultimately succinyl-CoA is produced which can feed into the CAC

Stimulated pathway when person has MCADD

20
Q

Odd chain beta-ox

A

After final reaction…propionyl-CoA is produced (instead of A-CoA)

Propionyl-CoA —> succinyl-CoA —> CAC

Two cofactors needed to do this…

  1. Biotin: used to add CO2 to the molecule —> methylmalonyl-CoA
  2. Vitamin B12: needed for a mutase to convert above product to succinyl-CoA
21
Q

Methylmalonic acidemia

A

Occurs when there is a problem with the mutase in the odd-chain ox reaction to make succinyl-CoA from propionyl-CoA

22
Q

Oxidation of very long chain FAs (VLCFAs)

A

Occurs in the peroxisome

2 aspects that differ from normal ox…

  1. Transport of VLCFAs into the peroxisome does not require carnitine
  2. Initial oxidation reaction that produces FADH2 (side product)…will oxidize back to FAD…and O2 —> H2O2

***NADH and Acetyl-CoA still produced each round

VLCFAs —> medium and short chains…leave the peroxisome as carnitine derivatives —> enter mito to undergo normal FA

23
Q

Zellweger syndrome

A

Elevated VLCFAs

Inability to target peroxisome matrix proteins to the peroxisome

24
Q

X-linked adrenoleukodystrophy

A

Elevated VLCFAs

Inability to transport molecules such as VLCFAs across peroxisomal membrane

25
Q

Alpha-oxidation

A

For branched chain FAs

Occurs in peroxisome

Enzyme: alpha-hydroxylase
—> introduces a -OH group on alpha carbon (branch on beta carbon)
—> COOH group is then removed
** alpha carbon is now the new carboxyl carbon
**now the branch is on the alpha carbon
—> normal beta-ox yields propionyl-CoA (instead of Acetyl-CoA)

2nd round = acetyl-CoA

3rd round = branch on alpha carbon again —> so propionyl-CoA

4th round = acetyl-CoA and sooooo on….

LAST round = 4C isobutyryl-CoA

**recall: propionyl-CoA is converted to succinyl-CoA then goes to CAC

26
Q

Refsum disease

A

Genetic defect in phytanoyl-CoA hydroxylase

= alpha-hydroxylase involved in the alpha-ox of phytanic acid…

Therefore unable to oxidation the branched points on that FA

High levels of phytanic acid in blood and tissues —>

Severe neurological problems

Restrict foods rich in this acid

Biochemistry Cardio (13 decks)

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