Breakdown and Synthesis of Amino Acids

Question 1

Breakdown of serine

Answer 1

Serine Direct/Self Deamination

Serine Dehydratase

1) Dehydrates the OH group to form double bond
2) deaminates serine by adding H2O to produce Pyruvate and Amonnium
- Amonnium is not transferred to Alpha-Ketogluterate

Question 2

Breakdown of Threonine

Answer 2

Threonine Direct/Self Deamination

Threonine Dehydratase

1) Dehydrates the OH group to form double bond
2) Deaminated threonine by adding H2O to product alpha-ketobutyrate and NH4+
- Ammonium is not transferred to Alpha ketogluterate

Question 3

Which amino acids are broken down to Acetyl CoA and AcetoAcetyl CoA

Answer 3

Aliphatic Branched chains (Leucine, Isoleucine, and Lysine

Aromatic Amino Acids (Tryptophan, Tyrosine, Phenylalanine)

Question 4

Breakdown of Phenylalanine

Answer 4

Aromatic amino acid so requires oxidases

1) Phenylalanine-> Tyrosine
- via Phenylalanine Hydroxylase (monoxygenase)
- Tetrahydrobiopterin-electron carrier; converted to quinonoid biopterin
- O2-> H2O

2) Transamination-Amino group converted to Keto group
- product p-hydroxyphenylpyruvate

3) P-hydroxyphenylpyruvate hydroxylase (dioxygenase)
- produced HOMOGentisate

4) Homogentisate Oxidase (dioxygenase)
- ring opening
4) isomerization
5) Hydrolyzed to produce FUMURATE AND ACETOACETATE-> AcetoAcetyl CoA

Question 5

Breakdown of Tryptophan

Answer 5

Aromatic amino acid so requires Oxidases
**converted to alanine and acetoacetate via several oxidases

1) Tryptophan -> Ringopening of 5C double bond ring via dioxygnease
2) Aldehyde reduced to amino group
3) Oxygenase
- adds OH beside Amino group
4) Alanine is released
5) Dioxygenase acts upon
- 11 steps later forms acetoacetate

Question 6

Glutamate Breakdown

Answer 6

-Demaminated into alpha ketogluterate

Glutamate Dehydrogenase
2 Step Process:
1) Glutamate is oxidized to form Schiff Base, NAD+ reduced to NADH
2)Schiff Base Intermediate which is hydrolyzed to produce a Keto group to form alpha ketogluterate and NH4+ is released

Question 7

Gln breakdown

Answer 7

1) Glutamine-> Glutamate
- Hydrolyzed via Glutaminase

2) Glutamate-> Alpha ketogluterate
Glutamate dehydrogenase
2 Step Process:
1) Glutamate is oxidized to form Schiff Base, NAD+ reduced to NADH
2)Schiff Base Intermediate which is hydrolyzed to produce a Keto group to form alpha ketogluterate and NH4+ is released

Question 8

Proline Breakdown

Answer 8

1) Proline is converted to Glutamic y-semialdehyde (2 steps)
2) Glutamic Y-semialdhyde is oxidized to Glutamate
3) Glutamate-> Alpha Ketogluterate

2 Step Process:

1) Glutamate is oxidized to form Schiff Base, NAD+ reduced to NADH
2) Schiff Base Intermediate which is hydrolyzed to produce a Keto group to form alpha ketogluterate and NH4+ is released

Question 9

Arginine Breakdown

Answer 9

1) Arginine -> Ornithine + urea
- Hydroxlyzed by Arginase
- ornithine transported into matrix of mitochondria
2) Ornithine-> Glutamic y-Semialdehyde
- R group amine oxidized to Aldehyde
3) Glutamic y-semialdehyde oxidized to Glutamate
4) Glutamate-> Alpha ketogluterate

2 Step Process:

1) Glutamate is oxidized to form Schiff Base, NAD+ reduced to NADH
2) Schiff Base Intermediate which is hydrolyzed to produce a Keto group to form alpha ketogluterate and NH4+ is released

Question 10

Histidine Breakdown

Answer 10

Multistep process with 4- imidazolone-5-proprionate intermediate
-then to glutamate-> alpha Ketogluterate

2 Step Process:

1) Glutamate is oxidized to form Schiff Base, NAD+ reduced to NADH
2) Schiff Base Intermediate which is hydrolyzed to produce a Keto group to form alpha ketogluterate and NH4+ is released

Question 11

Valine Breakdown

Answer 11

1) Valine-> Propionyl CoA
2) Propionyl CoA -> Methylmalonyl CoA
- via Propionyl Carboxylase
- Prosthetic Group-biotin
3) Methylmalonyl CoA-> Succinyl CoA
- Methylmalonyl CoA mutase
- Vit B12 (Cobalamin)

Question 12

Isoleucine Breakdown

Answer 12

1) Isoleucine-Propionyl CoA
2) Propionyl CoA -> Methylmalonyl CoA
- via Propionyl Carboxylase
- Prosthetic Group-biotin
3) Methylmalonyl CoA-> Succinyl CoA
- Methylmalonyl CoA mutase
- Vit B12 (Cobalamin)

Question 13

Methionine Breakdown

Answer 13

1) Methionine + ATP-> S-Adenosyl Methionine(SAM)
2) SAM donates activated methyl group to form S-Adenyosyl Homocysteine
3) S-Adenosyl Homocystein Hydrolyzed to Homocystein
- releasing Adenosine
4) Homocysteine + Serine -> Cystathionine
- via Cystathionine Synthase
5) Cystathionine-> alpha-ketobutyrate + Cysteine
- via Cytathioninase Hydrolyzes
5) Alpha Ketobutyrate-> Propionyl CoA
6) Propionyl CoA -> Methylmalonyl CoA
- via Propionyl Carboxylase
- Prosthetic Group-biotin
7) Methylmalonyl CoA-> Succinyl CoA
- Methylmalonyl CoA mutase
- Vit B12 (Cobalamin)

Question 14

Aspartate Breakdown

Answer 14

Direct Deamination into OAA

Aspartate-> OAA

• Aspartate Transaminase + PLP
• alpha amino group transferred to alpha ketogluterate to form Glutamate

Question 15

Asn Breakdown

Answer 15

1) Asparagine-> Aspartate
- Asparaginase-hydrloyzes to remove NH4+ of R group
2) Asprate-> OAA
- Aspartate Transaminase + PLP
- alpha amino group transferred to alpha ketogluterate to form Glutamate

Question 16

Glutamine Synthesis

Answer 16

Glutamine Synthetase

1) Glutamate Phosphorylated to acyl Phosphate Intermediate
2) Ammonia (NH3+) displaces the phosphate producing Glutamine

Question 17

Aspartate Synthesis

Answer 17

Aspartate Transaminase
-PLP
OAA + Glutamate-> Aspartate + Alpha ketogluterate

Question 18

Alanine Synthesis

Answer 18

Alanine Transaminase
-PLP
Pyruvate + Glutamate-> Alanine + Alpha ketogluterate

Question 19

Asparagine Synthesis

Answer 19

Asparagine Synthetase
**Adenylation

1) Aspartate-> Acyl-Adenylate Intermediate
2) NH3+ from Glutamine displaces the AMP producing Asparagine

Question 20

Arginine Synthesis

Answer 20

1) Glutamate phosphorylated to Acyl-Phosphate intermediate
2) Acyl Phosphate intermediate is reduced to Glutamic Acid y-semialdehyde and NADPH -. NADP+
3) Glutamic acid Y-semialdehyde -> Ornithine (urea cycle) to produce Arginine
- Glutamate-> Alpha ketogluterate to provide amino group

Question 21

Proline Synthesis

Answer 21

1) Glutamate phosphorylated to Acyl-Phosphate intermediate
2) Acyl Phosphate intermediate is reduced to Glutamic Acid y-semialdehyde
3) Nonenzymatic reaction dehydrates Glutamic Acid Y-semialdehyde and then reduced to Proline by NADPH

Question 22

Serine Synthesis

Answer 22

1) 3-PG oxidized to 3-Phosphohydroxypyruvate
- NAD+ reduced to NADH
2) 3-Phosphohydroxypyruvate -> 3-Phosphoserine
- amino transfered from glutamate to Alpha ketoglutarate
3) 3-Phosphoserine Hydrolyzed to Serine

Question 23

Glycine Synthesis

Answer 23

1) Serine hydroxymethyl transferase
-reversing this enzyme can be used to synthesize serine from glycine
-allows one carbon units to be synthesized from carbohydrates
Precursor: Serine
Serine + THF-> Glycine + N5,n10-methyleneTHF + H2O

2) Serine/Glycine Synthase
Precursor: NH4 + CO2
-NH4+ CO2+ N5,N10 methyleneTHF + NADH->Glycine + THF +NAD+

Question 24

Cysteine Synthesis

Answer 24

1) Homocysteine+ Serine-> Cystathionine
- Cystathionine B-Synthase
- LOse OH and bond to S of homocystein
2) Cystathionine-> Alpha ketobutyrate + Cysteine
- Cystathioninase

Question 25

Activated Methyl Cycle

Answer 25

Regenerates Methionine from homocysteine

1) SAM donates activated methyl group producing S-adenosyl homocysteine (
2) S-adenosyl Homocysteine is hydrolyzed
- releassing Adenosine and producing Homocysteine
3) Homocysteine is methylated via N,5methyl THF to produce methionine + THF
- Via Methionine Synthase (Homocysteine methyltransferase)
- requires methylcolbalamin derived from vitamin B12
- Some organisms use enzyme that don’t require methylcobalamin

Question 26

Tyrosine Synthesis

Answer 26

1) Phe BH4-> Tyr + quinonoid dihydrobiopterin
- Phenyalanine Hydroxylase (monooxygenase)
- BH4-tetrahydrobiopterin-electron carrier