Amino Acid Metabolism Flashcards
Where can amino acid metabolism occur?
- Peripheral tissues
- Liver
What are the two general steps of amino acid catabolism?
Step 1: Removal of amino group (nitrogen)
Step 2: Carbon skeleton
Approximately how many grams of free amino acids are located in the amino acid pool?
100-200 grams
Where is most of the free amino acid pool found?
In intracellular skeletal muscle
What are the two methods that amino acids are transported throughout the body?
- Free amino acid concentration gradient
- Active transport systems (ATP)
Does taking a lot of one amino acid limit the intake of others sharing the same transporter? True or False?
True, it may limit the intake
What is absorbed faster, peptides or free amino acids?
Peptides are absorbed faster
Can nitrogen be stored in the body?
No
In order to be removed, where is nitrogen first sent?
The liver
What are the two processes used to remove amino groups?
Transamination and Oxidative Deamination
What form is nitrogen excreted as?
Urea
Where does transamination occur?
Liver and peripheral tissues
What is the amino group acceptor of transamination?
alpha-ketoglutarate
What is the product of transamination after alpha-ketoglutarate accepts an amino group?
Glutamate and an alpha-keto acid
What is the required enzyme of transamination?
Pyridoxal phosphate (derivative of vitamin B6)
Aminotransferases are the main enzyme used in transamination. What are the three types?
- Muscle alanine aminotransferase (ALT)
- Liver alanine aminotransferase (ALT)
- Aspartate aminotransferase (AST)
What is the other name for Muscle/liver alanine aminotransferase and aspartate aminotransferase?
- Glutamate-pyruvate tranaminase (GPT)
- Glutamate oxaloacetate transaminase (GOT)
Where does oxidative deamination occur?
Liver and kidney
Overall what occurs during oxidative deamination?
An ammonia group is released as a free ammonia
What is the main enzyme of oxidative deamination?
Glutamate dehydrogenase
What are the main exports of muscles to the liver?
- Glutamine (glutamate + ammonia)
- Alanine
What enzyme is used to create glutamine?
Glutamine synthetase
Which cycle does the liver utilize to deal with ammonia?
Urea cycle
This enzyme deaminates glutamate.
Glutamate dehydrogenase (GDH)
This enzyme transfers amino groups from glutamate to oxaloacetate and eventually forms aspartate.
Aspartate aminotransferase (AST) or otherwise known as glutamate oxaloacetate transaminase (GOT)
This is the main entry point into the urea cycle.
CO2+NH3+2ATP–>carbamyol phosphate
Enzyme: carbomoyl phosphatase
Location: Mitochondrial matrix
What are the steps of the urea cycle?
Carbamoyl phosphate+ornithine–>citrulline
Citrulline–>argininosuccinate (use aspartate)
Argininosuccinate–>arginine (lose fumarate)
Arginie–> ornithine (lose urea)
Enzyme 1: ornithine transcarbamoylase
Enzyme 2: argininosuccinate synthase
Enzyme 3: argininosuccinate lyase
Enzyme 4: arginase
After it is made, where is urea sent to be excreted?
- Transported in the blood to the kidneys
- Some ammonia diffuses back into the blood, sent to GI tract, and excreted in feces
How many nitrogen molecules does urea have and what is the precursor to these molecules?
Two: one from aspartate and one from free NH3
-Glutamate is the precursor to both
When the amino acid group is removed from an amino acid, what is left?
Alpha-ketoacid
What happens to an alpha ketoacid depends on what four things?
- Energy charge
- Hormones (glucagon/insulin)
- Glucose concentration
- Tissue (liver vs. muscle)
What happens to amino acids when there is a low energy charge?
The amino acid is oxidized to recreate ATP
What happens to amino acids when there is low glucose?
The amino aicd is sent to the liver to turn into glucose
What happens to amino acids when there is a high energy charge and lots of glucose?
The amino acid is sent to the liver and turned into fat
What are three key amino acid conversions that can directly enter the aerobic system?
- AlaninePyruvate
- GlutamineGlutamatealpha-ketoglutarate
- AsparagineAspartateOxaloacetate
What are the two amino acids that cannot turn into glucose?
Leucine and lysine (ketogenic)
Skeletal muscle is only able to significantly oxidize six amino acids. What are they?
- Leucine
- Isoleucine
- Valine
- Glutamate
- Aspartate
- Asparagine
Out of the six amino acids that skeletal muscle is able to oxidize, which are branch chain amino acids?
- Leucine
- Isoleucine
- Valine
What amino acid has the highest intracellular/extracellular ratio?
Glutamate
What happens to plasma concentrations of glutamate and alanine during exercise?
- Glutamate decreases
- Alanine increases
In the absence of nutrient intake, what serves as the principal reservoir to replace blood amino acids taken up by other tissues?
Muscle protein
What enzyme converts glutamate into glutamine?
Glutamine synthetase
What enzyme converts glutamine back into glutamate?
Glutaminase
What are the most abundantly released amino acids in muscle?
Glutamine and Alanine
