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Biochemistry II > Amino metabolism - AA III > Flashcards

Amino metabolism - AA III Flashcards

1
Q

As a summary..

Which AAs are degraded to pyruvate?

A
  • Trp → Ala
  • Gly → Ser
  • Cys

REMEMBER: pyruvate → OXA

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2
Q

How can Ala be converted to pyruvate?

A

via ALAT = reversible transamination
α-KG + Ala → glu + pyruvate

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3
Q

What are the 2 pathways how Ser can be synthesized?

Where does it happen?

A

from

  • 3-P-glycerate (intermediate of glycolysis)
    → in cytoplasm
  • Gly by the action of Ser hydroxymethyl transferase
    → in mitochondrium

<u>NOTE:</u> SHMT catalyzes also reverse reaction, hence synthesis and degradation to another AA

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4
Q

How is Ser synthesized in the cytosol?

Where does it happen?

List its 3 steps.

A

synthesized from 3-P-glycerate in cytosol

  1. 3-P-glycerate → 3-P-pyruvate
  2. …. → 3-P-Ser
  3. …. → Ser
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5
Q

Which enzyme catalyzes the first step of synthesis of Ser from 3-P-glycerate?

Reaction + structures.

A

P-glycerate dehydrogenase

3-P-glycerate + NAD+ → 3-P-pyruvate + NADH

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6
Q

Which enzyme catalyzes the conversion of 3-P-pyruvate to eventually synthesize Ser?

Reaction + structures.

A

P-serine transaminase
transamination of 3-P-pyruvate, 3-P-Ser formed

3-P-pyruvate + Glu → 3-P-Ser + α-KG

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7
Q

Which enzyme catalyzes the conversion of 3-P-Ser to synthesize Ser?

Reaction + structures.

A

P-Ser phosphatase

3P-Ser + H2O → Ser + Pi

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8
Q

What are the 4 mechanisms of degradation of Ser?

Products.

A
  • to pyruvate
    • ​Ser-Thr ​dehydratase
    • Ser-pyruvate aminotransferase
  • to Cys: cystathione synthase/lyase:
  • to Gly: Ser hydroxymethyl transferase

<u>NOTE:</u> SHMT catalyzes also reverse reaction, hence synthesis and degradation to another AA

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9
Q

How can Gly be synthesized?

Enzyme + reaction.

Where does it happen?

A

Ser hydroxymethyl transferase = SHMT
this isoenzyme in cytosol

Ser + H4F ⇔ CH2-H4F + Gly + H2O

NOTE: can be considered part of catabolizing pathways of Ser, or anabolizing pathway of Gly

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10
Q

What is the physiological role of Gly?

A
  • inhibitory NT in NS
  • used for purine synthesis
  • conjugates, e.g. bile acids
  • heme biosynthesis
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11
Q

Where are the isoenzymes of SHMT located?

Function.

A
  • cytosolic SHMT: Ser → Gly
  • mitochondrial SHMT: Gly → Ser
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12
Q

As a summary..

What is the importance of SHMT?

A
  • synthesis of Gly from 3P-glycerate (through Ser)
  • synthesis of Ser from Gly
  • synthesis of methyl-group donor
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13
Q

What is the prosthetic group of SHTM?

A

PLP

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14
Q

How is the CH2-H4F that is necessary for the synthesis of Ser from Gly generated?

Which enzyme catalyzes this reaction?

A

Gly cleavage complex
degrades a second Gly

Gly + H4F + NAD+
→ HCO3- + NH4+ + CH2-H4F + NADH

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15
Q

What is the cause of nonketotic hyperglycinemia?

Consequences?

A

deficiency of Gly cleavage complex

→ mental deficiency, early death

Gly = inhibitory NT​

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16
Q

Ser is pretty important for cell membranes.

Why?

A

can be used to form

  • sphyngosine → incorporated into sphyngolipids
  • ethanolamine
  • choline
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17
Q

What is the biogenic amine of Ser?

Reaction + structures.

Function?

A

ethanolamine

Ser → ethanolamine + CO2

= second-most-abundant head group of phospholipids

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18
Q

As a summary…

Which AAs are converted to acetoacetate?

A

acetoacetate → acetyl CoA

  • Lys
  • Leu
  • Phe → Tyr
  • Trp
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19
Q

Which enzyme catalyzes the formation of choline?

Reaction + structures.

Function?

A

SAM dependent methylase

ethanolamine + 3 SAM → choline + 3 SAH

→ forms part of phospholipids

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20
Q

As a review..

How is Cys synthesized?

Which enzymes in its formation?

A

cystathione synthase/lyase
replace Ser-OH attached to HomoCys by -SH in 2 step reaction

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21
Q

What are the 2 degradational pathways of Cys?

What is the final product?

A

either degraded to

  • 3-mercapto pyruvate, or
  • sulfinyl pyruvate

→ eventually oxidized to pyruvate

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22
Q

Which enzymes are responsible for the formation of sulfinyl pyruvate?

Reaction steps + structures.

Which structures does it eventually form?

A

synthesized in 2 steps from Cys

  1. cysteine dioxygenase: Cys → Cys-sulfinate
  2. transamination:… → sulfinyl pyruvate

⇒ forms pyruvate + bisulfite

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23
Q

How is 3-mercapto pyruvate synthesized?

Which structures does it eventually form?

A

formed via transamination from Cys

⇒ -SH forms thiosulfite + pyruvate

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24
Q

How is sulfate formed?

Differentiate btw its 2 pathways.

A

originally derived from Cys

  • 3-mercapto pyruvate → thiosulfite
  • Cys sulfinate → sulfinyl-pyruvate → bisulfite

⇒ form sulfate

25
What is PAPS? How is it formed? Reaction + structure.
**_= activated sulfate_** formed in 2 steps 1. sulfate + ATP → AMPS + PPi 2. AMPS + ATP → PAPS + ADP + Pi ​⇒ most common coenzyme for sulfotransferase reactions
26
How is taurine synthesized? Reaction + structures. Functions?
_biogenic amine of Cys_ 1. Cys sulfinate → CO2 + **hypotaurine** 2. hypotaurine + 1/2 O2 → **taurine** **​**⇒ conjugation of bile acids + cytoprotective function in brain
27
As a summary... Which AAs are degraded to α-KG?
* **Gln → Glu** * **His, Arg, Pro →** Glu
28
What are the common intermediates of synthesis _AND_ degradation of Orn, Arg, and Pro?
_form together w/ Gln Glu family_ = all 3 AAs can be converted to Glu * **Δ1-pyrroline-5-carboxylate** * **Glu-γ-semialdehyde** (spontaneous interconversion)
29
As a review.. How is Arg degraded? Structures.
_in urea cycle conv. to Orn_ → **Arg, Orn: same pathway** of synth./degr. 1. Orn transaminated to **Glu-γ-semialdehyde** 2. dehydrogenated to **Glu, NADPH**
30
How is proline degraded? Enzymes?
1. oxidized by **_POX_** → **Δ1-pyrroline-5-carboxylate** 2. spontaneous conversion → **Glu-γ-semialdehyde** 3. dehydrogenated → **Glu, NADPH** **​**_NOTE:_ dehydrogenation of Pro to its first product yields _ROS_
31
What is the physiological role of Glu in the brain?
* **Glu** = most important excitatory NT can be used to synthesize its biogenic amine * **GABA** = most important inhibitory NT
32
How is Glu produced in the brain?
* _from **glucose +** (mostly) **BCAAs**_ **_​_**glucose conv. to α-KG, BCAAs then used for transamination * _restored in **glutamine cycle**_ *(cf. own card)* after synpatic transmission
33
What is the function of the glutamine cycle in the brain?
removes Glu from synapse after synaptic transmission, converted to Gln, shuttled back into neuron 1. Glu enters **cytosol of astrocyte** 2. conv. by cytosolic **Gln synthetase** Glu + ATP + NH4+ → Gln + ADP + Pi 3. Gln released into extracellular space, taken up by **neuron** 4. conv. by mitochondrial **glutaminase** Gln + H2O → Glu + NH4+
34
What is the GABA shunt?
**GABA degraded to Glu and succinate** → shunt bc reaction mediated by α-KG DEH in citrate cycle (α-KG → succinyl CoA) bypassed | (only in presence of α-KG)
35
Describe the mechanism of the GABA shunt. Which enzymes are involved?
_happening in 3 steps_ last 2 steps mediate inactivation of GABA 1. **_Glu decarboxylase_** Glu → CO2 + GABA 2. **_GABA transaminase_** GABA + α-KG → Glu + succinate semiald. 3. **_succinate semiald. DEH_** succinate semiald. + NAD+ + H2O → succinate + NADH
36
What is the physiological relevance of Arg?
* intermediate in **urea cycle** (forms Orn) * **activator of Nac-Glu synthase** * used for **creatine** synthesis * used for **NO** synthesis
37
Describe the mechanism of creatine synthesis.
happens via intermediate _guanidinoacetate_ (GAA) 1. **Arg + Gly** → **Orn + GAA** 2. **SAM + GAA** **→ SAH + creatine**
38
Describe the 2 step reaction of creatinine formation. Enzyme + reaction.
1. **_creatine kinase_** creatine + ATP → creatine-P + ADP 2. _dephosphorylated_ **creatine-P → creatinine + Pi** ⇒ then excreted via urine
39
What is the physiological relevance of Orn?
* intermediate in **urea cycle** * can used for synthesis of **polyamines**
40
List the 3 polyamines. What is their function?
* **putrescine** * **spermidine** * **spermine** ​⇒ show amphipathic structure, able to interact w/ DNA and proteins to regulate cell cycle and apoptosis
41
Which enzyme catalyzes the production of histamine? Reaction. What is the function of histamine?
= biogenic amine of His **_His decarboxylase_** His → CO2 + histamine _functions:_ * bronchoconstriction *(via H1-R)* * release of NO from endothelium *(via H1-R) →* vasodilation * release of HCl from parietal cells *(via H2-R)*
42
As a summary... Which AAs are degraded to fumarate?
* **Phe → Tyr** * **Asp** (aspartate cycle not relevant)
43
Which enzyme catalyzes the synthesis of Tyr? Reaction. What is the consequence?
**_Phe hydroxylase_** **Phe + O2 + H4-biopterine → H2-biopterine + Tyr + H2O** _NOTE:_ only Phe essential, since Tyr can be synthesized from it
44
What is the product of catabolism of Tyr? Name 1 important intermediate.
degraded to **homogenisate** → **acetoacetate/fumarate**
45
What is the cause of PKU? Consequence, treatment.
**_deficiency of Phe hydroxylase_** Tyr becomes essential, Phe degraded to * phenyl-pyruvate * phenyl-lactate * phenyl-acetate → excreted via urine ⇒ ketoacidosis, mental retardation, can be treated w/ Phe free diet
46
What is the physiological relevance of Tyr?
* precursor of **melanine** * precursor of **catecholamines** (dopamine, nor-/epinephrine) * precursor of **thyroid hormones T3, T4**
47
List the steps of the synthesis of catecholamines. Where does it happen? Differentiate btw the cellular locations of the different steps.
synthesized from Tyr in adrenergic postggl. axon terminals, adrenal medulla 1. **Tyr → dopa** 2. ... → **dopamine** 3. ... → **norepinephrine** 4. *.*.. → **epinephrine** ALL in cytosol, except step 3
48
Which enzyme is responsible for the _first_ step of the synthesis of catecholamines? Reaction + structures. Where does it happen?
**_Tyr hydroxylase_** in cytosol **Tyr + O2 + H4-biopterine → dopa + H2O + H2-biopterine** basically same reaction as Phe hydroxylase
49
What is the cofactor for the reaction catalyzed by Phe hydroxylase? How does it regain its original structure once it participiated in the formation of Tyr?
**H4-biopterine** → H2-biopterine ⇒ _dihydrobiopterine reductase_ H2-biopterine + NADPH → H4-biopterine + NADP+ ⇒ **cofactor of Phe, Trp, Tyr hydroxylase**
50
Which enzyme catalyzes the conversion of DOPA in the formation of catecholamines? Reaction + structures. Where does it happen?
**_DOPA decarboxylase_** in cytosol ## Footnote **DOPA → dopamine + CO2**
51
What is the prosthetic group of DOPA decarboxylase?
**PLP** PLP = prost. group of all decarboxylases
52
Which enzyme catalyzes the conversion of dopamine in the formation of catecholamines? Reaction + structures. Where does it happen?
**_dopamine β-hydroxylase_** only reaction happening in vesicle, hence dopamine must be imported first ## Footnote **dopamine + O2 → norepinephrine + H2O**
53
Which enzyme is responsible for the _fourth_ step of the synthesis of catecholamines? Reaction + structures. Where does it happen?
**_NE N-methly-transferase_** (= SAM dep. methyltransferase) in cytosol ## Footnote **norepinephrine + SAM → epinephrine + SAH**
54
What is the physiological relevance of Trp? Can it be synthesized in the body?
* precursor of **NAD+** * used for synthesis of **serotonin, melatonin** ​⇒ essential
55
What are the products of degradation of Trp?
* **Ala** * **formate** → formyl H4F (purine synthesis) * **NAD+ precursor** * further alternative pathways
56
Describe the synthesis of serotonin. Reaction + structures.
_biogenic amine of Trp_ 1. _**Trp hydroxylase** ​_Trp + O2 + H4-biopterine → 5-OH-Trp + H2O + H2-biopterine 2. **_5-OH Trp decarboxylase_** 5-OH-Trp → CO2 + serotonin (5-HT) NOTE: 1. reaction = similar to Phe/Tyr hydroxylase reaction
57
As a summary.. Which AAs are non-essential, ergo can be synthesized?
_10_ * **Ala, Asp, Asn** * **Cys** * **Glu, Gln, Gly** * **Pro** * **Ser** * **Tyr** **​**AAA C GGG ProST
58
As a summary.. What is the only semi-essential AA?
**Arg**
59
As a summary.. List all essential AAs.
_9/10_

Biochemistry II (16 decks)

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