Amino Acid Catabolism and the Urea Cycle

Question 1

What are activators and inhibitors of glutamate dehydrogenase?

Answer 1

Inhibitors = ATP and GTP
Activators = ADP and GDP (if energy levels are low in the presence of sufficient amino acids, oxidative deamination of glutamate is stimulated and promotes amino acid catabolism into TCA cycle intermediates

Question 2

What does Carbamoyl phosphate synthetase I (CPSI) do?

Answer 2

Converts CO2 + NH3 + 2ATP —-> Carbamoyl phosphate

Question 3

What does Ornithine transcarbamoylase do?

Answer 3

Converts L-Ornithine –> L-Citrulline

Question 4

What does Argininosuccinate synthase do?

Answer 4

Once L-Citrulline is transferred from the mitochondria it is converted to Argininosuccinate

Question 5

What does argininosuccinate lyase do?

Answer 5

Converts Argininosuccinate to L-Arginine

Question 6

What does Arginase do?

Answer 6

Converts L-Arginine to UREA!

Question 7

What is the rate limiting step in the urea cycle?

Answer 7

The enzyme carbamoyl phosphate synthetase I? It is allosterically activated by N-acetyl glutamate

Question 8

What does glutamine synthetase do?

Answer 8

Uses ammonia and glutamate to make glutamine in extra-hepatic tissues

Question 9

Once Glutamine is synthesized by glutamine syntheses in the tissues what happens?

Answer 9

The Glutamine is then transported to the liver where GLUTAMINASE produces ammonia and glutamate

Question 10

Extra-hepatic amino groups can also be transportered to the liver through the glucose-alanine cycle. Where does this occur?

Answer 10

THE MUSCLE.

Question 11

What are some characteristics of urea cycle disorders?

Answer 11

Hyperammonemia, Encephalopathy and respiratory alkalosis