Nitrogen Metabolism

Question 1

Is there any nitrogen storage in the body?

Answer 1

NO

Question 2

Nitrogen balance-3 possibilities

Answer 2

1. Balanced: normal adult
2. Positive: increase in protein synthesis (normal in children)
3. Negative: Catabolic response to trauma/starvation

Trauma leads to stress hormones-mobilization of carbon skeletons

Question 3

What are the Essential Amino Acids?

Answer 3

Arginine
Leucine
Histidine
Isoleucine
Tryptophan
Threonine
Methionine
Phenylalanine
Valine

“A Little Humility In Learning Ten Tiny Molecules Proves Valuable”

Question 4

Ketogenic Amino Acids

Answer 4

Yields:
* Acetoacetate
* Acetyl CoA
* Acetoacetyl Coa

Leucine, Lysine

“Losers”

Question 5

Both Glucogenic and Ketogenic

Answer 5

Threonine
Tyrosine
Tryptophan
Isoleucine
Phenyalanine

“TTTIP”

Question 6

Glucogenic Amino Acids

Answer 6

Glycine
Serine
Glutamate

Not comprehensive

Question 7

What is the process of removing an amino group?

Answer 7

Transaminiation
Products are:
1. Alpha Ketoglutarate
2. Glutamate

Question 8

What are the two amino acids that do not participate in transamination?

Answer 8

1. Threonine
2. Lysine

Question 9

Alanine aminotransferase (ALT)

Answer 9

Also called: Glutamate-pyruvate transaminase (GPT)
* present in liver in highest concentrations
* readily reversible
* glutamate acts as a collector of nitrogen from alanine

Question 10

Aspartate aminotransferase (AST)

Answer 10

Also called: Glutamate-oxaloacetate transaminase (GOT)
* Found in a variety of tissues
* Forms aspartate which is used a nitrogen source in the urea cycle

Question 11

Oxidative deamination pathway

Answer 11

• Liberates ammonia and a-keto acid (liver and kidney)
• Glutamate dehydrogenase (mitochondrial)

Question 12

What are the 7 products from the breakdown of C-skeleton of amino acids

Answer 12

1. Oxaloacetate
2. a-ketoglutarate
3. Pyruvate
4. Fumarate
5. Succinyl CoA
6. Acetoacetyl CoA
7. Acetyl CoA

Question 13

Where is urea produced?

Answer 13

In the liver and transported in urea to the kidney for excretion in urin

Question 14

Where are the two nitrogens in the urea cycle from?

Answer 14

Both from glutamate
1. Transamination
2. Oxidative deamination

Question 15

Where is arginase found in the body?

Answer 15

ONLY IN THE LIVER

Question 16

How many ATP does it take for 1 molecule of NH3?

Answer 16

3 ATP

Question 17

Regulation of the Urea Cycle

Answer 17

• N-acetyl glutamate: essential allosteric activator of CPS I (RLS in mitochondria)
• Increases after ingestion of protein-rich meal (glutamate/arginine)

Question 18

What are the 6 sources of ammonium?

Answer 18

1. Amino Acids-produced in many tissues
2. Glutamine via renal glutaminase-important for acid-base balance
3. Glutamine via intestinal mucosal cells
4. Bacterial action in intestine breakdown urea in the intestine to ammonia
5. Amines breakdown of neurotransmitters
6. Purines/Pyrimidines Catabolism of amino groups

Question 19

Transport of ammonia in circulation (2)

Answer 19

1. Urea: Most important transport system of ammonia. Transported from liver to kidney
2. Glutamine: non-toxic storage and transport of NH3. Mostly in muscle and liver

Question 20

Acquired hyperammonemia: Alcoholism/Hepatitis/Biliary obstruction

Answer 20

May cause collateral circulation around liver

Question 21

Acquired hyperammonemia: Reye’s Syndrome

Answer 21

1. Occurs primarily in children w/ chickenpox or influenza AND given salicylates
2. Leads to mitochondrial damage and disruption of urea cycle
3. High levels of serum transaminase

Question 22

Hereditary hyperammonemia (1 in 30,000 births)

Answer 22

Genetic deficiency of any 1/6 of the urea cycle enzyes
* Results in mental retardation
* Death soon after birth

Question 23

Urea Cycle Overview

Answer 23