What is the product of the oxidation of this fatty acid?
What is the product of the oxidation of this fatty acid?
Fatty acids are carboxylic acids with a hydrocarbon chain ranging from 4 carbon to 36 carbons. Straight chain fatty acids undergo beta-oxidation to produce acetyl CoA and electron carriers such as NADH and FADH2 that are used up during cellular respiration to generate ATP.
Beta oxidation:
- The enzyme fatty acyl-CoA synthase (FACS) adds a CoA group to the fatty acid chain to form acyl-CoA.
- The enzyme acyl CoA dehydrogenase oxidizes the acyl-CoA. There is a formation of a double bond between 2C and 3C. the end product is called trans-Δ2-enoyl-CoA. FAD is reduced to FADH2 in this step.
- Enoyl CoA hydratase adds a hydroxyl group to the 2C of trans-Δ2-enoyl-CoA to form L-β-hydroxyacyl CoA
- The 3-hydroxyacyl-CoA dehydrogenase catalyzes the oxidation of L-β-hydroxyacyl CoA to β-ketoacyl CoA and reduces NAD+ to NADH.
- β-ketoacyl CoA is cleaved by β-ketothiolase between 2C and 3C to produce acetyl-CoA and new acyl CoA This acetyl CoA is made up of carbon 1C and 2C
- The new acyl-CoA chain which is now two carbons shorter will enter the second beta-oxidation cycle and with each cycle, it will be 2 carbons shorter.
During beta-oxidation, an even-numbered fatty acid with an 'X' number of carbon in the hydrocarbon chain will undergo an (X/2 - 1) cycle of oxidation and per cycle will produce 1 Acetyl CoA + 1 NADH + 1 FADH2. The last cycle will produce 2 acetyl CoA. Beta oxidation of odd-numbered fatty acids produces a propionyl CoA in the last cycle and it undergoes another round of oxidation to form succinyl CoA that enters TCA.
The presence of a methyl group on the beta carbon makes beta-oxidation of such fatty acids an impossibility. Instead, they undergo alpha oxidation.
- An acyl-CoA synthase adds a CoA group to the fatty acid chain. The product is an acyl-CoA.
- An acyl CoA hydroxylase adds a hydroxyl group to the alpha carbon using Fe2+ and O2. the product will be an alpha-hydroxy-acyl-CoA
- alpha-hydroxy-acyl-CoA will be split into formyl-CoA and an aldehyde due to the action of alpha-hydroxy-acyl-CoA lyase.
- An aldehyde dehydrogenase will convert the aldehyde into a carboxylic acid and reduces NAD(P)+ to NAD(P)H.
- The fatty acid left is now 1 carbon short with the methyl group on alpha carbon and can undergo beta-oxidation.
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