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Medical Biochemistry > Degradation of Amino Acids 2: The Fate of the Carbon Core > Flashcards

Degradation of Amino Acids 2: The Fate of the Carbon Core Flashcards

1
Q

Fate of carbon core of amino acids

A
  1. Fed: energy resources
    • Glycogen, TAG
  2. Fasting: energy production
    • Co2
    • Pyr
    • TCA intmd.
    • Acetyl CoA, acetoacetate
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2
Q

Degdation of amino acids

A
  • Glucogenic AA → TCA intmd or PYR →LIVERGlucose
  • Ketogenic AA → Acetoacetate or Acetyl CoA →LIVER KB
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3
Q

Conditionally essential AA

A

The sulfur of cysteine comes from methionine

Tyrosine is produced from phenylalanine

Arginine is not essential for adults, but it is essential for children

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4
Q

Outline of non-essential AA synthesis

  • Core of non-essential aa (10)
  • Tyrosine (1)
A

The carbon cores of 10 non-essential amino acids derive from glucose.

Tyrosine is produced by the hydroxylation of phenylalanine

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5
Q

Coenzymes in amino acid metabolism

transamination & deamination

A

Pyridoxal-Phosphate (B6)

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6
Q

Coenzymes in amino acid metabolism

Methionine metabolism

A

Cobalamins (B12)

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7
Q

Coenzymes in amino acid metabolism

Hydrxylation of phenylalanine, tyrosine and tryptophan

A

Tetrahydrobiopterin

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8
Q

Coenzymes in amino acid metabolism

Oxidative decarboxylation of BCAA

A

Thiamine-Pyrophosphate (B1)

and

Lipoate

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9
Q

Antileukemic drug

A

Asparginase

Asn is required for the growth of fast dividing cells.

  1. Asn A→ Asp B→ OXA
    • (AsparginaseA , ASTB )
    • Recall: AST converts 2-ketoglutrate to Glu, and Asp to OXA)
  2. Asp → Purines and pyrimidines → RNA/ DNA (of fast dividing leukemic cells.
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10
Q

AA’s that are degraded to a-ketoglutarate (aKGlu)

A

Glu, Gln, Pro, Arg, His

Gln → Glu ⇔ aKGlu

Arg → Ornithine ⇔ Glu semialdehyde → Glu ⇔ aKGlu

Proline → Glu semialdehyde → Glu ⇔ aKGlu

Histidine → FIGLu → Glu ⇔ aKGlu

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11
Q

FIGlu levels (urine)

Pts with follic acid deficiency

A

Patients with folic acid deficiency excrete increased amounts of FIGlu in their urine.

FIGlu excretion is used to monitor folic acid deficiency

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12
Q

Histidinemia

Biomarkers Blood and urine

Hint (histidine metabolism)

A

Deficiency in histidase (an enzyme for histidine metabolism)

Biomarker: Elevated levels of histidine in both blood and urine

His A→ Urocanic acid →→ FIGlu THF→ Glu→ a-Ketoglutarate

A - Histidase

Note: Patients with folic acid deficiency (tetrahydrofolate) excrete increased amounts of FIGlu in their urine

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13
Q

Histamine synthesis

rxn

Enzyne

A

Histidine Histidine Decarboxylase→ Histamine + CO2

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14
Q

AA that are degraded to pyruvate

A

Thr → Gly ⇔ Ser → Cys→ pyruvate ⇔ Ala

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15
Q

purines, creatine, heme and gluthathione all are synthesized from this amino acid as precursor

A

Gly

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16
Q

Primary rxn that produces glycine in the brain is synthesized by this enzyme

A

Serine hydrozymethyl transferase

Serine + THF Serine hydroxymethyl Transferase ⇔ Glycine

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17
Q

AA that are degraded to fumarate

A

Phenylalanine → Tyrosine →→→ Malylacetoacetate→ Fumarylacetoacetate

Fumarylacetoacetate → fumarate + acetoacetate

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18
Q

Tyrosinemia Type I

Deficient enzyme

Biomarkers

Spc. characteristics

Liver and kidney status

Tx

A

Fumarylacetoacetate(FAA) X→ fumarate + acetoacetate

deficiency of. fumaryl acetoacetate hydrolase

Accumulation of FAA and succinyl acetone in urine

Cabage like odor

Liver failure

Renal tubular acidosis

Tx: diet restriction of phenyl alanine and tyrosine

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19
Q

Alkaptonuria

A

Disease of the tyrosine degradation pathway.

Due to homogentisic acid oxidase deficiency.

Homogentisic acid accumulates in urine and tissues

Homogentisic acid accumulation in cartilage causes crippling arthritis (dense black deposits).

Urine turns dark within minutes

Scalera bluish-black pigment (generally the first sign) and in the cartilage of the ear.

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20
Q

Oculocutaneous Albinism Type 1

A
  • Due to tyrosinase deficiency
  • White skin, white hair, pink eyes
  • Eye and skin sensitive to sunlight
  • Nystagmus, far or near-sightedness
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21
Q

Biologically important metabolites of Tyrosine

A
  • Melanin (req. tyrosinase)
  • Catecholamine (req. tyrosine hydroxylase and BH4)
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22
Q

PKU

Causes

Tx

A

Deficient phenylalanine hydroxylase

Mutations in the enzyme

Insufficient tetrahydrobiopterin (BH4)

Treatment: Phe-restricted, Tyr supplemented diet

Avoid aspartame, artificial sweetener

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23
Q

PKU Sx

A
  • Elevated phenylalanine, phenylpyruvate, phenyllactate and phenylacetate in blood and urine (musty odor of urine).
  • Neurological problems (mental retardation,seizures, tremors, microcephaly etc) due to reduced production of catecholamines.
  • Hypopigmentation (light skin, hair, blue eyes) due to reduced melanin production.
24
Q

The role of tetrahydrobiopterin in neurotransmitter synthesis

Severity of its deficiency

A

Necessary for hydroxylation of:

  • Phenylalanine (tyrosine production)
  • Tyrosine (first step of catecholamine synthesis)
  • Tryptophan (first step of serotonin and melatonin synthesis)

Note: BH4 deficiency causes more severe phenylketonuria than mutations in phenylalanine hydroxylase

25
Amino acids that are degraded to Succinyl CoA
Methionine, threonine, valine and isoleucin
26
A- Brief summary of the rxn of aa degredation to succinyl CoA, and indicate how each of the following aas feed into it 1. methionine 2. threonine 3. valine 4. isoleucin B- List the diseases that might occur along these pathways
**a-KGlu**→ **propionyl CoA** →methylmalonyl CoA→ Succinyl CoA 1. methionine ⇒ a-Kglu 2. threonine → a-KGlu 3. Valine ⇒methylmalonyl semialdehyde →Priopionyl CoA 4. isoleucine⇒ methylmalonyl semialdehyde →Priopionyl CoA B- Organic acidimia, which leads to secondary hyperammonemia * methylmalonic acidemia * propionic acidemia
27
Diseases associated with the following pathway aa degradation to succinyl CoA
Organic acidemia (general term) → 2ndhyperammonemia Methylmalonic acidemia and priopionic acidemia
28
Causes of the following conditions: 1. methylmalonic acidemia 2. propionic acidemia
Propionyl CoA Carboxylase-Biotin → → methylmalonyl CoA **Mutase B12**→ Succinyl CoA 1. ***Priopionyl CoA carboxylase*** deficiency 2. ***Methylmalonyl CoA mutase*** deficiency
29
Priopionyl CoA carboxylase deficiency
priopionic acidemia (aa degdatation to succinyl CoA) Organic acidemia due to **elevated levels of 3-OH propionic acid** Organic acidimia leads to secondary hyperammonemia
30
Methylmalonyl CoA mutase deficiency
methylmalonic acidemia (aa degdradation to succiny CoA) ## Footnote elevated levels of **methylmalony acid in blood**
31
Methionine metabolism Homocystine Formation
S-Adenosylmethionine (SAM) is the **primary methyl donor** in the human body. It participates in the synthesis of: * phosphatidylcholine (cell membrane lipid) * creatine (muscle energy metabolism) * carnitine (fatty acid degradation) * melatonin (sleep-wake hormone) * epinephrine ("flight and fright" hormone)
32
The biosynthetic reactions that rely on S-adenosylmethionine as primary methyl donor
* phosphatidylcholine (cell membrane lipid) * creatine (muscle energy metabolism) * carnitine (fatty acid degradation) * melatonin (sleep-wake hormone) * epinephrine ("flight and fright" hormone)
33
Methionine metabolism : **formation of homocysteine** Rxn
L-methionin → SAM→ SA-homocystine → homocystine ## Footnote SAM: S-Adenosyl Methionione SA: S-adenosyl
34
Homocystinuria management:
Homocystinuria management: Restrict methionine, supplement cysteine
35
Methionine metabolism: degradation of homocystine ## Footnote Name 2 key enzymes and diseases assoicated with their dificiencies
Homocystine **Cistathione Synthase**→Cystathionine Cystathionase→ Cistine * **Cistathione synthase deficiency- Cyctathioninuria** * elevated **U. homocystine** * elevated **bld. methionina** * **Cystathionase dificiency- homocystinuria** * elevated cystathionine
36
High level of _**bld** homocysteine_ is a risk factor for
myocardial infarction
37
The cofactors required for **_transsulfuration rxns_** that lead to **cystine formation** (from homocystine) Hint: methionine degradation
**pyridoxine- B6**
38
Methionine metabolism : degradation of homocysteine What are the requirement for **remethylation rxns**? * Cofactor * Coenzyme
Cofactor: **folate** Coenzymes: **B12 derived coenzymes**
39
BCAA determine ketogenic or glucogenic
**Valine, Isoleucin and leucin** 1. Valine- Glucogenic 2. Isoleucine- Glucogenic **and** ketogenic 3. Leucine- Ketogenic
40
rxn type that is catalyzed by **a-ketoacid dehydrogenase**
oxidative decarboxylation
41
Factors required for proper functioning of **a-ketoacid dehydrogenase** ## Footnote **(BCAA metabolism)**
**Just like** Pyruvate dehydrogenase complexes ***(PDH)*** it requires 5 cofactos: 1. TPP 2. lipoate 3. FAD 4. NAD 5. CoASH a-ketoacid dehydrogenase participate in **oxidative decarboxylation** reactions.
42
The first and second reactions of BCAA metabolism Reactants Products Enzymes and their cofactors The end products made from each BCAA
BCAA **Transamination**⇔ a-ketoacid ** a-ketoacid dehydrogenase**⇒ X-CoA + CO2 + NADH ## Footnote a-ketoacid dehydrogenase req. TPP, Lipoate, NAD, FAD, CoASH Valine (Glucogenic) metabolism ► succinyl CoA Leucine (Ketogenic) metaboliosm ► acetoacetate and acetyl CoA Isoleucine ( ketogenic and glucogenic) ►acetyl CoA and succinyl CoA
43
Maple syrup urine disease (MSUD) I Love Vermont Maple Syrup * Dx * Sx * Tx
Dx Elevated BCAAs, especially **leucine**, in **blood**. Elevated branched-chain ketoacids (BCKA) in **blood** and **especially in urine**. Sx: Maple syrup odor of urine (by 5-7 days after birth) and of earwax (12-24 hr after birth). Encephalopathy (lethargy, poor feeding, apnea, opisthotonus, coma) **_BCAA restricted_** high calorie diet. Usually BCAA-free formulas, supplemented with limited amounts BCAAs. **Leucine** is always the **most restricted**. **All BCAAs are essential amino acids.**
44
MSUD Tx
BCAA restricted high calorie diet. Usually BCAA-free formulas, supplemented with limited amounts BCAAs. Leucine is always the most restricted. BCAAs are essential.
45
Pellagra Causes and manifestation
Lack of **tryptophan** and **niacin** (vitamin B3) in diet causes pellagra (characterized by the **4 Ds** – **D**ermatitis, **D**iarrhea, **D**ementia and if untreated **D**eath).
46
Tryptophan metabolism
Lack of tryptophan and niacin (vitamin B3) in diet causes pellagra (characterized by the 4 Ds – Dermatitis, Diarrhea, Dementia and if untreated Death).
47
Diseases of AA metabolism General Concepts
vRare diseases (incidence is generally less than 1:2,000). Can be caused by - - Mutated enzymes (autosomal recessive). - Insufficient co-factors. Many have **neurological symptoms**. AAs are precursors of neurotransmitters and hormones Early detection and treatment is a **must!!!** Many require **dietary adjustment in protein** consumption.
48
ketogenic family of amino acids
WIFY LK WIFY are both ketogenic and glucogenic LK only ketogenic W- Trp I- Ile F- Phe Y- Tyrosine L- Leucin K- Lysine
49
Amino acids that are both ketogenic and glucogenic
WIFY Trp-Ile, Phe, Tyr
50
Acetyl Coa Family of aa ## Footnote (based on the point where their C skeleton enter the TCA cycle) Determine the essential aa's
_**W*I*F***_Y_**L*K***_ ## Footnote W-Trp (essential) I-Ile (essential) F-Phe (essential) Y-Tyr L-Leu (essential) K- Lys (essential)
51
a- Ketoglutrate family of aa (based on the point where their C skeleton enter the TCA cycle)
_**H***_Q REP H-His (essential) Q- Gln (Glutamine) R- Arg E- Glu (Glutamate) P-Proline
52
Succinyl CoA Family of AA ## Footnote (based on the point where their C skeleton enter the TCA cycle)
VIM ## Footnote Val (essential) Ile (essential) Met (essential)
53
Fumarate Family of Amino Acids ## Footnote (based on the point where their C skeleton enter the TCA cycle)
FY ## Footnote F-Phe Y-Tyr
54
Oxaloacetate Family of AA ## Footnote (based on the point where their C skeleton enter the TCA cycle)
ND ## Footnote Asn- N Asp- D
55
Pyruvate Family of AA ## Footnote (based on the point where their C skeleton enter the TCA cycle)
CAST GW Cys- Ala- Ser-_Thr*_-Gly-_Trp*_ Thr and Trp are essential aa.
56
rxn fascilitated by the **methyl group** of Met
methylation reactions as **S*****-adenosylmethionine*** SAM Met SAM Synthetase→ SAM **Methyl Transferase**→ SAH

Medical Biochemistry (12 decks)

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