Lecture 8 - Amino Acid Catabolism Flashcards
Which enzymes cleave peptide bonds?
Proteases
Are amino acids stored?
Nope
What is the purpose of amino acid metabolism?
To get the nitrogen out of the amino acid and into urea for excretion
In general terms, what is the first step of amino acid catabolism?
Removal of the amino group from the carbon skeleton by transamination and deamination
What happens to the amino group of an amino acid in the liver?
Amino groups are transferred to alpha-ketoglutarate, which converts the amino acid to a ketoacid and the alpha-ketoglutarate to glutamate
_____ and _____ are converted to glutamate in the liver
Alanine and glutamine
Where are alanine and glutamine degraded?
Muscle and other tissues
Define transamination
Transferring the NH3 group from an amino acid to a ketoacid
What does transamination require?
Pyridoxal phosphate (PLP)
Define deamination
Removal of the NH3 group, generating free NH3
What accompanies deamination?
Redox reaction using NAD or NADP
Which molecules are always involved in transamination reactions?
Glutamate and alpha-ketoglutarate
What is the enzyme that is used in transamination reactions?
(Name of amino acid being converted) transaminase
What is the delta G value of transaminase reactions and what does this mean?
- delta G = 0
- They are fully reversible
What is significant about the structure of pyridoxal phosphate?
The pyridine ring allows for movement of electrons from NH+
Where is pyridoxal phosphate attached to the enzyme and when is it released?
- Attached at lysine
- Released for reaction to occur
Which amino acid is most commonly deaminated?
Glutamate
Which enzyme is involved in the deamination of glutamate?
Glutamate dehydrogenase
Which cofactors are needed for the deamination of glutamate?
NAD+ + H2O -> NADH + H+
What is produced in the deamination of glutamate?
Alpha-ketoglutarate
Is the deamination of glutamate reversible?
Yes
Which enzyme is involved in the deamination of alanine?
Alanine dehydrogenase
Which cofactors are needed for the deamination of alanine?
NAD+ + H2O -> NADH + H+
What is produced in the deamination of alanine?
Pyruvate and NH3
What is involved in an amino acid oxidase?
Amino acid is converted to an alpha-ketoacid
What are the cofactors needed in an amino acid oxidase reaction?
O2 + H2O -> NH3 + H2O2
What occurs in the most common deamination route?
Transamination is used to generate glutamate, and then glutamate undergoes deamination
Describe the deamination of aspartate
- Non-oxidative
- Enzyme used is asparate alpha-deaminase
- Produces fumarate and NH3
Describe the deamination of serine
- Non-oxidative
- Enzyme used if serine dehydratase
- Produces pyruvate and NH3
What is produced from oxidative deamination in muscle?
Ammonia
What does transamination of amino acids in muscle cause?
Buildup of glutamate
What is the function of glutamine in the blood?
Principle carrier of excess NH4
How is glutamate converted to glutamine?
- Enzyme is glutamine synthetase
- Cofactors are NH3 in and ATP -> ADP + Pi
How is glutamine converted to glutamate?
- Enzyme is glutaminase
- Cofactor is H2O -> NH4+
What happens to the released NH4?
Enters the urea cycle
_____ is the main route for the removal of NH4 from glutamate
Glutamate dehydrogenase
____ is a secondary NH4 carrier
Alanine
Where does alanine transport NH4?
From muscle to liver
_____ is the main route for the removal of NH4 from alanine
Alanine dehydrogenase
What happens to excess NH3?
Converted to urea and excreted
Why is NH3 harmful?
High [NH3] activates glutamate dehydrogenase/glutamine synthetase, producing glutamate and glutamine, which uses up ATP/NADH and can be damaging to the brain
