Lecture 9 - Valine Example

Question 1

Step 1

Answer 1

Valine -> alpha-keto isovalerate

Question 2

Step 2

Answer 2

Alpha-keto isovalerate -> isobutyryl CoA

Question 3

Step 3

Answer 3

Isobutyryl CoA -> methyl acrylyl CoA

Question 4

Step 4

Answer 4

Methyl acrylyl CoA -> beta-hydroxy isobutyryl CoA

Question 5

Step 5

Answer 5

Beta-hydroxy isobutyryl CoA -> beta-hydroxyl-isobutyrate

Question 6

Step 6

Answer 6

Beta-hydroxyl-isobutyrate -> methyl malonyl semi-aldehyde

Question 7

Step 7

Answer 7

Methyl malonyl semi-aldehyde -> propionyl CoA

Question 8

Step 8

Answer 8

Propionyl CoA -> succinyl CoA

Question 9

Enzyme for step 1

Answer 9

Branched chain amino acid-transaminase

Question 10

Enzyme for step 2

Answer 10

Alpha-ketoacyl dehydrogenase

Question 11

Enzyme for step 3

Answer 11

Acyl CoA dehydrogenase

Question 12

Enzyme for step 4

Answer 12

Enoyl CoA hydratase

Question 13

Enzyme for step 5

Answer 13

Beta-hydroxy isobutyryl CoA hydratase

Question 14

Enzyme for step 6

Answer 14

Beta-hydroxy isobutyryl dehydrogenase

Question 15

Enzyme for step 7

Answer 15

Methyl malonyl semi-aldehyde dehydrogenase

Question 16

Enzyme for step 8 (3 enzymes)

Answer 16

1) Propionyl CoA carboxylase
2) Methyl malonyl CoA epimerase
3) Methyl malonyl CoA mutase

Question 17

Cofactor for step 1

Answer 17

Alpha-ketoglutarate -> glutamate

Question 18

Cofactor for step 2

Answer 18

• CoASH in
• NAD+ -> NADH + H+
• CO2 out
• TPP, FAD

Question 19

Cofactor for step 3

Answer 19

FAD -> FADH2

Question 20

Cofactor for step 4

Answer 20

H2O in

Question 21

Cofactor for step 5

Answer 21

• H2O in

- CoASH out

Question 22

Cofactor for step 6

Answer 22

NAD+ -> NADH + H+

Question 23

Cofactor for step 7

Answer 23

• NAD+ -> NADH + H+

- CoASH in

Question 24

Cofactor for step 8

Answer 24

None

Question 25

What is alpha-ketoacyl dehydrogenase similar to with respect to cofactors?

Answer 25

Pyruvate dehydrogenase

Question 26

What is important about the enzymes used for step 8?

Answer 26

They are used in fatty acid oxidation of odd-numbered chain fatty acids

Question 27

What happens if alpha-keto acyl dehydrogenase is missing as a result of a genetic defect?

Answer 27

- The alpha-keto acids from valine, leucine, and isoleucine will accumulate in the blood and urine, impairing brain and nerve cell development - Maple syrup urine disease

Question 28

What happens after step 8?

Answer 28

- Succinyl-CoA is converted to oxaloacetate, which is then converted to pyruvate, then acetyl CoA, which then enters the TCA cycle - Total process produces 4 CO2