Amino Acid Degradation Flashcards
Four events involved in formation of urea
- Transamination and formation of alanine & glutamate
- Transport of nitrogen into the liver
- Transamination and Deamination in liver
- Ureas cycle
Where is the urea cycle
In hepatoctyes
In what two compartments of the cells does the urea cycle span
Mitochondria and cytsol
Function of transaminases
Transfer an amino group from one molecule to another
Two main amino acids from which an amino group is taken during transamination
Alanine and Aspartate
Which molecule is the removed amino group usually transferred to
alpha- ketoglutarate
Which new amino acid is usually formed during transamination
glutamate
Which transaminase is used which alanine
Alanine transaminase
Which transaminase is used which aspartate
Aspartate transaminase
Which substance is needed to mediate transfer during transamination
Pyridoxal phosphate (PLP)
What is pyridoxal phosphate derived from
Vitamin B6
Which two amino acids do not participate in transamination
Lysine and threonine
What two substances in amino acid metabolism in a clinical indicator for liver damage
Aspartate transaminase and Alanine transaminase
Which molecule transports amino acid nitrogen to the liver
Glutamine
Which two molecules combine to form Glutamine
Glutamate and ammonia
Which enzyme is needed for the formation of glutamine
Glycine synthetase
Which tissues require glutamine to transport nitrogen to the liver
Brain, muscle and adipose tissue
What is the importance of glutamine in the brain
To remove excess nitrogen and prevent ammonia toxicity
Two processes by which ammonia is obtained for the urea cycle
Deamination of glycine and oxidative deamination of glutamate
Which reaction requires glutaminase
Conversion of glutamine to glutamate
Which reaction requires glutamate dehydrogenase
Conversion of glutamate to alpha-ketoglutarate
Which of the two reaction that sequesters ammonia is reversible
Conversion of glutamate to alpha-ketoglutarate
Where does detoxification of ammonia occur
liver
The nitrogen atoms contained in urea come from which substances
free ammonia and aspartate
How is aspartate formed
Transamination of glutamate with oxaloacetate in the presence of AST
How is ammonia formed in the intestine
Bacterial urease makes ammonia
How is ammonia produced in the intestine transported to the liver
Travels through portal blood to the liver
Four immediate sources of ammonia for the urea cycle
- Deamination of glutamine
- Oxidative deamination of glutamate
- Bacterial urease in intestine
- Transamination of glutamate with oxaloacetate
Six main products of the urea cycle
- carbamoyl phosphate
- Citrulline
- Argininosuccinate
- Argininosuccinate
- Urea
- Ornithine
What activates N-acetylglutamate synthase
Arginine
Function of acetylglutamate synthase
Coverts glutamate to acetylglutamate
What activates Carbamoyl
phosphate
synthetase I
N-acetylglutamate
Starting molecules for the urea cycle
NH4, HCO3, 2ATP
What converts Carbamoyl phosphate to Citrulline
Ornithine
transcarbamoylase
What converts Citrulline to Argininosuccinate
Argininosuccinate
synthetase
What converts Argininosuccinate to Arginine
Argininosuccinate
lyase
When aspartate gives up its amino group in the urea cycle what molecule does it become
Fumarate
What converts Arginine to Ornithine
Arginase
When is urea produced in the urea cycle and what enzyme controls this step
Conversion of Arginine to Ornithine with the enzyme arginase
At which steps in the urea cycle are ATP molecules utilized
- Conversion of Carbamoyl phosphate to Citrulline
2. Conversion of Citrulline to Argininosuccinate
Causes of hyperammonemia
- Congenital hyperammonemia
- Acquired hyperammonemia
- Liver disease (alcohol cirrhosis, hepatitis)
- Shunting of blood from portal system to systemic circulation
Which inherited disease of the urea cycle is X-linked recessive
Ornithine Transcarboxylase deficiency
How does Ornithine Transcarboxylase deficiency lead to excretion of orotic acid
Carbamoyl phosphate builds up and enters the cytosol to go into pyrimidine synthesis which produces orotic acid
Treatments for hyperammonemia
- low protein diet
- Phenylbutyrate
- benzoic acid
How does Phenylbutyrate treat hyperammonemia
Phenylbutyrate gets converted to phenylacetate, which binds to glutamine for phenylacetylglutamate that gets excreted
How does benzoic acid treat hyperammonemia
Benzoic acid binds to glycine and turn into hippuric acid which gets secreted
