30 Questions
What is the characteristic of each aminotransferase?
Specific for one or a few amino group donors
What is the product of the reaction catalyzed by alanine aminotransferase (ALT)?
Glutamate and pyruvate
What is the role of aspartate aminotransferase (AST) in the urea cycle?
Source of nitrogen in the urea cycle
What is the coenzyme required for the activity of aminotransferases?
Pyridoxal phosphate
What is the mechanism of action of aminotransferases?
Transfer of amino group to the pyridoxal part of the coenzyme
What is the site of attachment of pyridoxal phosphate to the enzyme?
Specific lysine residue
What is the result of the oxidative deamination of glutamate?
Formation of corresponding keto acids and ammonia
What is the role of NAD+ in the oxidative deamination of glutamate?
To act as a co-enzyme
What is the direction of the reaction catalyzed by glutamate dehydrogenase dependent on?
The relative concentrations of glutamate, α-ketoglutarate, and ammonia
What is the reaction catalyzed by glutamate dehydrogenase in the presence of NADPH?
Reductive amination
What is the significance of elevated levels of aminotransferases in the plasma?
Indication of cell damage or death
Where does the oxidative deamination of glutamate occur?
Liver and kidney
What happens to glutamate levels in the liver after ingesting a meal containing protein?
Nigh elevated
Why is reductive amination necessary in the body?
To reduce ammonia levels
What is the role of GTP and ATP in glutamate dehydrogenase regulation?
Inhibitors
What is the primary disposal route of ammonia in the body?
Formation of urea in the liver
How does glutamine synthetase react with glutamate and ammonia?
Glutamate + ammonia = glutamine
What happens to glutamine in the liver?
It is cleaved by glutaminase
Which enzyme catalyzes the formation of citrulline?
Ornithine transcarbamylase
What is the primary function of the glucose-alanine cycle?
To allow muscles to use glucose from the liver
What is the rate-limiting step in the synthesis of urea?
Formation of carbamoyl phosphate
Where does the formation of citrulline take place?
Mitochondria
What is the source of the second amino group in urea?
Aspartate
How many ATP molecules are consumed in the first step of urea synthesis?
2
What is the total number of ATP molecules consumed in the formation of urea?
3
Which enzyme is responsible for cleaving argininosuccinate to yield arginine and fumarate?
Argininosuccinate lyase
What is the product of the reaction catalyzed by arginase?
Urea and ornithine
Where is the enzyme arginase mostly found?
Liver
What is the rate-limiting enzyme in the urea cycle?
Carbamoyl phosphate synthetase (CPS-I)
What is the activator of carbamoyl phosphate synthetase (CPS-I)?
N-Acetylglutamate (NAG)
Learn about the substrate specificity of aminotransferases, including their naming conventions and clinical importance, with a focus on alanine aminotransferase (ALT) and aspartate aminotransferase (AST).
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