Amino acid catabolism and ammonia production Flashcards
(33 cards)
Where are dietary proteins broken down and absorbed as amino acids?
In the gastrointestinal tract
What happens to amino groups from amino acids in the liver?
They are transferred to glutamate
How is alanine formed during amino acid catabolism?
Excess amino groups are transferred to pyruvate
How is excess NH4+ managed in peripheral tissues?
Converted to the sidechain nitrogen of glutamine
How is glutamine processed in the liver?
It is deaminated to release ammonia
What is the first step in catabolising most L-amino acids?
Removal of α-amino group
What is the common collecter of amino groups from various amino acids?
Glutamate
What cofactor do all aminotransferases use?
Pyridoxal phosphate (PLP), a form of vitamin B6
What reaction mechanism do aminotransferases follow?
Classic biomolecular ping-pong mechanism
How is ammonia released from glutamate?
Through oxidative deamination by glutamate dehydrogenase
What electron acceptors can mammalian glutamate dehydrogenase use?
NAD+ or NADP+
What regulates glutamate dehydrogenase activity?
GTP is a negative modulator
What syndrome is linked to GTP-binding site mutations in GDH?
Hyperinsulinism-Hyperammoneamia Syndrome
How is ammonia transported in the blood?
As glutamine
What is a condition caused by excess ammonia in the brain?
Hepatic encephalopathy
What enzyme incorporates ammonia into glutamine?
Glutamine synthetase
Why must ammonia be converted for excretion?
It is toxic; urea is non-toxic and efficient for nitrogen excretion
Where does the urea cycle occur?
Exclusively in the liver
What enzyme initiates the urea cycle?
Carbamoyl Phosphate Synthetase I
What are the two nitrogen sources entering the urea cycle?
Carbamoyl phosphate
Aspartate
What enzyme adds carbamoyl phosphate to otnithine?
Ornithine transcarbamylase
What enzyme intorduces the second amino group?
Argininosuccinate synthetase
What does argininosuccinase release?
Fumarate
What does arginase produce?
Urea
Regenerates ornithine
