BMP: FA B-oxidation

Question 1

Why is it called b-oxidation

Answer 1

Because the B-group of the FA undergoes oxidation to form a carbony group

Question 2

How many steps are involved in B-oxidation?

Answer 2

4

Question 3

What is step 1?

Answer 3

Step 1. Oxidation

The first dehydrogenation of fatty acyl Co A is catalysed by FAD dependent acyl CoA dehydrogenase, resulting in a trans Δ² fatty enoyl CoA and generation of one molecule of FADH₂.

Question 4

What is step 2

Answer 4

Step 2. Hydration

Enoyl CoA hydratase catalyses the conversion of trans Δ² fatty enoyl CoA to L‐β‐hydroxy acyl CoA, via hydration of the trans‐α, β double bond created in step 1.

Question 5

What is step 3?

Answer 5

Step 3. Oxidation

NAD dependent dehydrogenation via β ‐hydroxy acyl CoA dehydrogenase creates β keto acyl CoA and one molecule of NADH.

Palmitoyl Co A is 16 carbons long

Question 6

What is step 4?

Answer 6

Step 4. Thiolysis

Cleavage of the bond between the α and β carbon is catalysed by β ‐keto thiolase in the presence of co enzyme A (in the form of Co ASH). This results in a fatty acyl Co A which is 2 carbons shorter and a molecule of acetyl Co A. The fatty acyl Co A re‐enters the pathway, and will continue to do so until it is full oxidised. The number of times this happens therefore depends on fatty acyl chain length.

Question 7

What is the generic equatino for B-oxidation?

Answer 7

Question 8

What is the equations for B-oxidation of plamitoyl coA?

Including the final one

Answer 8

Question 9

What is the net gain of ATP?

Answer 9

106

(2 ATP used to convert palmitic acid to plamitoyl-coA)

Question 10

What happens during oxidation of an odd numbered FA?

Answer 10

• Most fatty acids have even chain number, although odd chain types are formed.
• Therefore the final round of b-oxidation yields 1 acetyl CoA and 1 propionyl CoA.
• Propionyl CoA is converted to succinyl CoA which enters the TCA cycle or used in ketone body catabolism.

Question 11

What ketone bodies is there?

Answer 11

• The ketone bodies acetoacetate and D-b-hydroxybutyrate are alternate metabolic fuels for peripheral tissue.
• Particularly brain and skeletal muscle.
• These are derived from acetyl CoA in hepatocyte mitochondria.

Question 12

During starvation what is used as an energy source?

Answer 12

• During starvation glucose is unavailable.
• Fatty acids cannot cross the blood-brain barrier and ketone bodies are the brain neurons major fuel source.
• Ketone body utilisation in brain tissue requires their conversion to acetylCoA, a process requiring either 2 or 3 reactions.

Question 13

How are ketones converted to acetyl coA?

Answer 13

1. D-b-hydroxybutyrate is oxidised to acetoacetate catalysed by D-b-hydroxybutyrate dehydrogenase.
2. Acetoacetyl CoA produced from acetoacetate by CoA transfer from a succinyl CoA donor, catalysed by succinyl CoA transferase.
3. Thiolysis of acetoacetyl CoA by thiolase (with CoASH), liberating 2 acetyl CoA.