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Dems Unit 02 - 02 > INtro Amino acids - disposal of Nitrogen 19 > Flashcards

INtro Amino acids - disposal of Nitrogen 19 Flashcards

1
Q

Any aa in excess of biosynthetic needs are rapidly degraded. First and second phase of catabolism involves?

A
  1. transamination via aminotransferase
    - removal of a-amino group grom a-amino acid
  2. oxidative deamination
    - forms ammonia and a-keto acid “carbon skeleton” of aa
  • presence of a-amino group keeps aa safe from oxidative breakdown.
  • a-ketoglutarate is the ammonia (amino group) acceptor and becomes glutamate
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2
Q

Cystinuria

A

carrier system is defective and cannot uptake COAL

  • cystine
  • ornithine
  • arginine
  • lysine

all 4 appear in urine
- most common genetic error of amino acid transport

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3
Q

transamination

A

funneling of amino group to glutamate

transfer a-amino group from a-amino acid to a-ketoglutarate –>
a-keto acid + glutamate

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4
Q

Two sources of urea nitrogen

A

ammonia

aspartate

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5
Q

Two most important aminotransferases

A

Alanine aminotransferase (ALT)

Aspartate aminotransferase ( AST)

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6
Q

ALT

- fxn

A

Alanine aminotransferase (ALT)

  • transfer amino group of alanine to a-ketoglutarate
  • generates pyruvate + glutamate

(glutamate is the “acceptor” of Nitrogen from alanine)
- readily reversible

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7
Q

AST

- fxn

A

Aspartate aminotransferase (AST)

  • transfers amino groups from aspartate to a-ketoglutarate
  • makes oxaloacetate and glutamate
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8
Q

aminotransferases require the coenzyme ____. Which is a derivative of ____.
Fxn?

A

pyridoxal phosphate (PLP)

  • derivative of Vit B6
  • “holds” the amino group during transfer
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9
Q

equilibrium constant of transamination rxn? Why is this imp?

A

K = 1

Allows rxn to fxn in both:

  1. aa degradation (via a-amino group removal) and
  2. aa biosynthesis (via addition of amino group to carbon skeleton of a-keto acid)
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10
Q

Why are elevated AST and ALT levels important?

A

Aminotransferases are normally intracellular enzymes

  • presence of elevated levels indicates dmg to cells rich in these enzymes
  • ALT more sensitive for liver than AST
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11
Q

Oxidative deamination of amino acids (ie: glutamate –> a-ketoglutarate) are done via which enzyme?

A

glutamate dehydrogenase

  • this frees an ammonia (NH3)
  • provides an a-keto acid for metab.

(usually in liver and kidneys)

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12
Q

Diff between transamination and oxidative deamination

  • enzyme
  • substrates
A

Sequential actions:

transamination

  • aminotransferases
  • transfer -NH2 of a-amino acid (with a-ketoglutarate) to glutamate

oxidative deamination

  • glutamate dehydrogenase
  • ox deam. of glutamate to regenerate a-ketoglutarate and release amino group as ammonia, and make NADH/NADPH (3 things)

These rxns also free up a-keto acids which can enter central pathway of E metabolism.

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13
Q

After ingestion of meal containing protein, glutamate levels _____ in the liver, and the transamination rxn proceeds in which direction?

A

Meal –> Glutamate rises

  • rxn proceeds in direction of aa degradation and formation of ammonia
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14
Q

GTP is an allosteric ______ glutamate dehydrogenase.
ADP is an allosteric _____ of glutamate dehydrogenase

(note that glutamate dehydrogenase is responsible for oxidative deamination of a-ketoglutarate and glutamate)

A

GTP: inhibitor

ADP: activator

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15
Q

When E levels are low (high ADP, low GTP), then glutamate dehydrogenase is _____.

A

High

this facilitates E production from the carbon skeletons derived from aa.

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16
Q

How do Hu transport ammonia from the peripheral tissue to the liver for its conversion to urea?

A
  1. Glutamate gets converted to Glutamine via Glutamine synthetase (which adds an extra NH3, and uses ATP doing so)
    - GLutamine is a nontoxic transporter of ammonia
  2. Glutamine is transported from most tissues –> blood –> Liver
  3. Glutamine in the liver is cleaved by glutaminase to make glutamate and free NH3 again!
  4. NH3 can be excreted as Urea in the liver
17
Q

How do amino acids in muscles contribute to making pyruvate in the liver to produce glucose?

A

GLucose-alanine cycle

Pyruvate in the muscle can be transaminated by ALT to alanine. Alanine can then move to blood to liver.

  • Ala is then tranaminated to pyruvate.
  • This pyruvate can be used to undergo gluconeogenesis and make glucose.
18
Q

Urea

A

major disposal form of amino groups derived from amino acids

  • accounts for 90% of nitrogen containing components of urine.
  • produced by the LIVER –> transported in the blood to kidneys for excretion in the urine
19
Q

Urea is supplied by which two nitrogens? What serves as the precursor to both nitrogens?

A
  1. free ammonia
  2. N of aspartate
  • glutamate is the immediate precursor of both ammonia
20
Q

First two rxns of Urea cycle

  • where
  • what
A

In mitochondria

  1. formation of carbamoyl phosphate
  2. formation of citrulline
21
Q

What substrate in the urea cycle has to form before its transfer from the mitochondria to the cytosol?

A

citrulline
(from Ornithine + carbamoyl phosphate via ornithine trans-carbamoylase)
- moves via cotransporter with ornithine (citrulline out, ornithine in)

22
Q

Places where ATP is consumed in urea cycle

A

1+2. first step of urea cycle
- CO2 + NH3 + 2ATP –> carbamoyl phosphate

  1. 3rd step
    - Citrulline + aspartate + ATP –> arginosuccinate
23
Q

Immediate precursor of urea

A

arginine (via arginase) –> urea
(from arginosuccinate)
- in LIVER

24
Q

RLS of the urea cycle

A

First step

N-Acetylglutamate is essential activator for Carbamoyl Phosphate synthetase I

25
Q

After ingestion of a protein rich meal, levels of N-acetylglutamate ______.

A

increases
This activates carbamoyl phosphate synthetase
- increased rate of urea synth.

26
Q

Hyperammonemia (ammonia intoxication) sx

A
  1. tremors
  2. slurring of speech
  3. somnolence
  4. vomiting
  5. cerebral edema
  6. blurred vision
  7. coma/death
27
Q

Acquired hyperammonemia

A

Conversion of ammonia to urea is severely impaired

liver disease is a common cause

  • ie: hepatitis, hepatotoxins (OH)
  • cirrhosis (portal blood shunted to systemic circulation with no access to liver)

*note: elevated glutamine always accompanies hyperammonemia bc its a nontoxic storage and transport form of ammonia

28
Q

COngenital hyperammonemia

A

Ornithine trans-carbamoylase deficiency

  • x-linked
  • failure to synthesize urea –> hyperammonemia in first weeks following birth
  • high morbidity

*note: elevated glutamine always accompanies hyperammonemia bc its a nontoxic storage and transport form of ammonia

29
Q

3 amino acid : a-keto acid pairs commonly encountered in metabolism

A

alanine/pyruvate

aspartate/oxaloacetate

glutamate/a-ketoglutarate

30
Q

amino nitrogen of dietary protein is excreted as ____

A

urea.

- urinary urea is increased by a diet rich in protein

31
Q

What significant part of the urea cycle takes place in the mitochondria?

A

CO2+ NH3 + 2ATP + carbamoyl phosphate synthetase I → carbamoyl phosphate

carbamoyl phosphate + Ornithine → Citrulline

32
Q

Urea cycle happens where?

A

Liver

33
Q

Glutamate dehydrogenase goes both ways ;) what two things does it interconvert?

A

Glutamate → a-ketoglutarate
and visa versa

*glutamate has NH3, a-ketoglutarate does not

Dems Unit 02 - 02 (20 decks)

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