Question

Look up the entire 4 step β-oxidation process for a fatty acid. a. (16) Show the reactions and enzymes used to degrade stearic acid by 2 carbons. b. (4) List all of the products from this set of reactions. c. (4) List all of the products if you were to oxidize the entire fatty acid. I.

Answer 1

ß-Oxidation occurs in Mitochondria, but fatty acids are impermeable to mitochondrial membrane. So, in order to make it permeable fatty acid undergo two step .

• Acyl CoA formation;

            Fatty acid + CoA+ATP ↔ Fatty-acyl CoA +AMP + PPi

Enzyme - Acyl CoA synthetase, a thioester linkage form between carboxyl group of fatty acid and thiol group of CoA.

• Carnitine transport;

Fatty acyl CoA get attached to the hydroxyl group of Carnitine and undergo a facilitated diffusion through acylcarnitine/ carnitine transporter

ß-Oxidation

First Stage:

• Dehydrogenation of fatty acyl CoA produces a double bond at α and ß position to form trans-2-enoyl CoA.
• In this a trans unsaturation has been inserted.
• The hydrogen ion is taken away by FAD.

Second Stage:

• A molecule of water is added to trans-2-enoyl CoA across α and ß double bond to form L- stereoisomer of ß-hydroxy acyl CoA.

Third Stage:

• L-ß-hydroxy acyl CoA is dehydrogenated in the presence of NAD to form ß-keto acyl CoA.

Fourth Stage:

• In this thiolysis happen by inducing a CoA which cause cleavage between α and ß forming two carbon acetyl CoA and Fatty acyl CoA (Myristol CoA) get reduced by two carbon.
• The process is continued seven such times

One Cycle
Stage	Enzyme	Product	Coenzyme	ATP
1st	Acyl CoA Dehydrogenase	Transenol CoA	FADH2	2
2nd	Enoyl CoA Hydratase	L-ß-hydroxyacyl CoA
3rd	ß-hydroxyacyl CoA Dehydrogenase	ß-ketoacyl CoA	NADH+H+	3
4th	Thiolase	Myristoyl CoA+Acetyl CoA	CoA	Acetyl CoA to TCA cycle

Complete Cycle
Acetyl CoA	8
FADH2	7
NADH	7
H+	7
ATP (TCA not included)	35