Oxidization

Information about Oxidization

Schematic demonstrating mitochondrial fatty acid beta-oxidation and effects of LCHAD deficiency

Beta oxidation is the process by which fatty acids, in the form of Acyl-CoA molecules, are broken down in the mitochondria and/or in peroxisomes to generate Acetyl-CoA, the entry molecule for the Krebs Cycle.

Occurs in mitochondrial matrix.

Four recurring steps

Once inside the mitochondria, the β-oxidation of fatty acids occurs via four recurring steps:

Description	Diagram	Enzyme	End product
Oxidation by FAD: The first step is the oxidation of the fatty acid by Acyl-CoA-Dehydrogenase. The enzyme catalyzes the formation of a double bond between the C-2 and C-3.		acyl CoA dehydrogenase	trans-Δ²-enoyl-CoA
Hydration: The next step is the hydration of the bond between C-2 and C-3. The reaction is stereospecific, forming only the L isomer.		enoyl CoA hydratase	L-3-hydroxyacyl CoA
Oxidation by NAD⁺: The third step is the oxidation of L-3-hydroxyacyl CoA by NAD⁺. This converts the hydroxyl group into a keto group.		L-3-hydroxyacyl CoA dehydrogenase	3-ketoacyl CoA
Thiolysis: The final step is the cleavage of 3-ketoacyl CoA by the thiol group of another molecule of CoA. The thiol is inserted between C-2 and C-3.		Β-ketothiolase	An acetyl CoA molecule, and an acyl CoA molecule, which is two carbons shorter

This process continues until the entire chain is cleaved into acetyl CoA units. For every cycle, one molecule of FADH₂, NADH and acetyl CoA are formed.

β-oxidation of unsaturated fatty acids

β-oxidation of unsaturated fatty acids poses a problem since the location of a cis bond can prevent the formation of a trans-δ² bond. These situations are handled by an additional two enzymes.

Whatever the conformation of the hydrocarbon chain, β-oxidation occurs normally until the acyl CoA (because of the presence of a double bond) is not an appropriate substrate for acyl CoA dehydrogenase, or enoyl CoA hydratase:

If the acyl CoA contains a cis-Δ³ bond, then cis-δ³-Enoyl CoA isomerase will convert the bond to a trans-Δ² bond, which is a regular substrate.
If the acyl CoA contains a cis-Δ⁴ double bond, then its dehydrogenation yields a 2,4-dienoyl intermediate, which is not a substrate for enoyl CoA hydratase. However, the enzyme 2,4 Dienoyl CoA reductase reduces the intermediate, using NADPH, into trans-Δ³-enoyl CoA. As in the above case, this compound is converted into a suitable intermediate by cis-Δ³-Enoyl CoA isomerase.

To summarize:

odd numbered double bonds are handled by the isomerase.
even numbered bonds by the reductase (which creates an odd numbered double bond) and the isomerase.

β-oxidation of odd-numbered chains

Chains with an odd-number of carbons are oxidized in the same manner as even-numbered chains, but the final products are propionyl CoA and acetyl CoA.

Propionyl CoA is converted into succinyl CoA (which is an intermediate in the citric acid cycle) in a reaction that involves Vitamin B12. Succinyl CoA can then enter the citric acid cycle.

Because it cannot be completely metabolized in the citric acid cycle, the products of its partial reaction must be removed in a process called cataplerosis. This allows regeneration of the citric acid cycle intermediates, possibly an important process in certain metabolic diseases.

Oxidation in peroxisomes

Fatty acid oxidation also occurs in peroxisomes. However, the oxidation ceases at octanyl CoA.

One significant difference is that oxidation in peroxisomes is not coupled to ATP synthesis. Instead, the high-potential electrons are transferred to O₂, which yields H₂O₂. The enzyme catalase, found exclusively in peroxisomes, converts the hydrogen peroxide into water and oxygen. It is believed that very long chain (C-22)fatty acids undergo initial oxidation in peroxisomes which is followed by mitochondrial oxidation. Peroxisomal oxidation is induced by high fat diet and administration of hypolipidemic drugs like clofibrate.

Energy yield

The ATP yield for every oxidation cycle is 14 ATP, broken down as follows:

Source	ATP	Total
1 FADH₂	x 1.5 ATP	= 1.5 ATP (some sources say 2 ATP)
1 NADH	x 2.5 ATP	= 2.5 ATP (some sources say 3 ATP)
1 acetyl CoA	x 10 ATP	= 10 ATP (some sources say 12 ATP)
TOTAL		= 14 ATP

For an even-numbered saturated fat (C_2n), n - 1 oxidations are necessary and the final process yields an additional acetyl CoA. In addition, two equivalents of ATP are lost during the activation of the fatty acid. Therefore, the total ATP yield can be stated as:

(n - 1) * 14 + 10 - 2 = total ATP

For instance, the ATP yield of palmitate (C₁₆, n = 8) is:

(8 - 1) * 14 + 10 - 2 = 106 ATP

Represented in table form:

Source	ATP	Total
7 FADH₂	x 1.5 ATP	= 10.5 ATP
7 NADH	x 2.5 ATP	= 17.5 ATP
8 acetyl CoA	x 10 ATP	= 80 ATP
Activation		-2 ATP
TOTAL		= 106 ATP

For sources that use the larger ATP production numbers described above, the total would be 129 ATP equivalents per palmitate.

External links

The chemical logic behind fatty acid metabolism at ufp.pt
JEREMY M. BERG,JOHN L. TYMOCZKO and LUBERT STRYER Biochemistry, 2002
Animations at brookscole.com

• • [ e] Lipid metabolism: Lipid metabolism/Fatty acid metabolism
Fatty acid degradation (Lipolysis, Beta oxidation) - Fatty acid synthesis

• • [ e] Metabolism: lipid metabolism
Lipid production	Acetyl-CoA carboxylase - Fatty acid synthesis: Beta-ketoacyl-ACP synthase - Β-Ketoacyl ACP reductase - 3-Hydroxyacyl ACP dehydrase - Enoyl ACP reductase unsaturated (Enoyl CoA isomerase, 2,4 Dienoyl-CoA reductase) - odd chain (Propionyl-CoA carboxylase) - Fatty acid synthase - Long fatty acyl CoA synthetase
Lipid degradation	Acyl transport: Carnitine palmitoyltransferase I - Carnitine-acylcarnitine translocase - Carnitine palmitoyltransferase II Beta oxidation: Acyl CoA dehydrogenase (ACADL, ACADM, ACADS, ACADVL) - Enoyl-CoA hydratase - 3-Hydroxyacyl CoA dehydrogenase - Acetyl-CoA C-acyltransferase - Mitochondrial trifunctional protein Ketogenesis: HMG-CoA synthase - HMG-CoA lyase - Other: Malonyl-CoA decarboxylase
Phospholipids	Diacylglycerol kinase
Steroids	HMG-CoA reductase - Farnesyl-diphosphate farnesyltransferase - Squalene monooxygenase - Lanosterol synthase - CYP51A1
Prostanoids	Cyclooxygenase - Thromboxane-A synthase - Prostacyclin synthase - Prostaglandin E synthase - Prostaglandin D2 synthase
Leukotrienes	Arachidonate 5-lipoxygenase - 5-Lipoxygenase activating protein - Leukotriene A4 hydrolase - Leukotriene C4 synthase
Bile acids	Cholesterol 7 alpha-hydroxylase

Types of Fats in Food

Unsaturated fat
Monounsaturated fat
Polyunsaturated fat
Trans fat
Omega: 3, 6, 9

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Peroxisomes are ubiquitous organelles in eukaryotes that participate in the metabolism of fatty acids and other metabolites. Peroxisomes have enzymes that rid the cell of toxic peroxides.
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Acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main use is to convey the carbon atoms within the acetyl group to Krebs Cycle to be oxidized for energy production.
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citric acid cycle, also known as the tricarboxylic acid (TCA) cycle, the Krebs cycle, or Szent-Györgyi-Krebs cycle (after Hans Adolf Krebs and Albert Szent-Györgyi who first determined the chemical intermediates and reaction sequence of the cycle), is a series
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Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed.

This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide, or the
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Flavin is a tricyclic heteronuclear organic ring based on pteridine whose biochemical source is the vitamin riboflavin. The flavin moiety is often attached with an adenosine diphosphate to form flavin adenine dinucleotide (FAD
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Covalent bonding is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds.
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Acyl CoA dehydrogenase is the enzyme used to catalyze the first step of β-oxidation in Fatty acid metabolism.

Reaction

The following reaction is the oxidation of the fatty acid by FAD.

The enzyme catalyzes the formation of a double bond between the C-2 and C-3.
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Hydration may refer to:

Rehydration, the replenishment of water and electrolytes lost through dehydration
The biological absorption of water by plant tissues, often resulting in a shape change.

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In organic chemistry, a hydration reaction is a chemical reaction in which a hydroxyl group (OH^-) and a hydrogen cation (an acidic proton) are added to the two carbon atoms bonded together in the carbon-carbon double bond which makes up an alkene functional group.
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In chemistry, stereospecificity is the property of a chemical reaction that yields different stereoisomeric reaction products from two stereoisomeric reactants depending on the reaction conditions.
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In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of chemical bonds between atoms, but in which the atoms are arranged differently (analogous to a chemical anagram).
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Enoyl-CoA hydratase is the enzyme used to catalyze the second step of β-oxidation in Fatty acid metabolism. It catalyzes the following reaction:

The reaction hydrates the bond between C-2 and C-3 on trans-Δ²-enoyl-CoA.
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Hydroxyl in chemistry stands for a molecule consisting of an oxygen atom and a hydrogen atom connected by a covalent bond. The neutral form is a hydroxyl radical and the hydroxyl anion is called a hydroxide.
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Keto can refer to:

The Keto people, an ethnic group of the Siberian North.
The keto group, the functional group in the chemical compounds ketones.
ketoconazole a medication that can inhibit the production of testosterone in both the testes and adrenal gland.

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3-Hydroxyacyl CoA dehydrogenase. This converts the hydroxyl group into a keto group.

The end product is 3-ketoacyl CoA.

External links

MeSH 3-Hydroxyacyl+CoA+Dehydrogenases

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Thiolysis is a reaction with a thiol (R-SH) that cleaves one compound into two. This reaction is similar to hydrolysis, which involves water instead of a thiol. This reaction is seen in β-oxidation of fatty acids.
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In organic chemistry, a thiol is a compound that contains the functional group composed of a sulfur atom and a hydrogen atom (-SH). Being the sulfur analogue of an alcohol group (-OH), this functional group is referred to either as a thiol group or a
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Coa can refer to:

Coa-A small village between Fermanagh and Tyrone

coa de jima, a specialized tool for harvesting agave cactus
Côa, a river in Portugal that is a major tributary of the Douro.

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Acyl CoA is a coenzyme involved in the metabolism of fatty acids. It is a temporary compound formed when Coenzyme A (CoA) attaches to the end of a long-chain Fatty Acid, inside living cells.
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Enoyl CoA isomerase (EC 5.3.3.8 ) is an enzyme that catalyzes conversion of cis-double bonds of fatty acids at position 3 to trans double bonds at position 2. It has a special importance in metabolism of unsaturated fatty acids.
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2,4 Dienoyl-CoA reductase is an enzyme on chromosome 8 involved in beta oxidation.

Pathology

Mutations can result in 2,4 Dienoyl-CoA reductase deficiency.

Source

It is an important intermediate in the citric acid cycle, where it is synthesized from α-Ketoglutarate by
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Oxidization

Information about Oxidization

Four recurring steps

β-oxidation of unsaturated fatty acids

β-oxidation of odd-numbered chains

Oxidation in peroxisomes

Energy yield

See also

External links

Reaction

External links

Pathology

See also

Source