Flashcards in Lecture 34 Deck (24):
What happens in the amino acids oxidase reaction? What is produced as a byproduct? What molecule is utilized?
- An amino acid oxidase liberates free ammonia from amino acids producing alpha-keto acid as a product
- H2O2 is produced as a byproduct - which is alarming
- FMN>FMNH2 (probably don't need to know this)
Why is excess ammonia bad?
toxic (is a base), as a metabolite can also screw up pathways
How is asparagine produced (what is the rxn)? Is it an essential AA?
- aspartate + glutamine + ATP = asparagine + glutamate + AMP + PPi
What enzyme converts asparagine to aspartate and releases an NH4 in the process? What else goes into the reaction?
What do amino acids transfer their amino group to as the first step in the urea cycle (and what is made)?
- react in an aminotransferase reaction with alpha-ketoglutarate to make glutamate
What are the two options for the NH3 on glutamate to enter the urea cycle in the liver?
1. Glutamate undergoes deamination via glutamate dehydrogenase to produce NH4 and alpha-ketoglutarate - the NH4 then combines with CO2 to form urea
2. Glutamate undergoes transamination with oxaloacetate to form aspartate and alpha- ketoglutarate - the aspartate is then converted to urea
How is carbamoyl phosphate formed? Where does the NH4 used in the reaction come from (what enzymes)? where does it fall on the urea circle diagram thing?
- HCO3- + NH4+ + 2 ATP = Carbamoyl phosphate + Pi
- NH4 comes from glutamate dhase or glutaminase
- first thing outside the circle
Where does the NH4 attached to aspartate (derived from transamination of glutamate) come into the urea cycle?
in the middle of the circle - right after citruline
What reaction requires ATP in the main circle of the urea cycle? How many enzymes required ATP in urea cycle?
- citrulline > argininosuccinate
What two compartments are involved in urea cycle? What happens where?
- mitochondria and cytoplasm
- carbomyl phosphate synthase and formation of citrulline occurs in mitochondria - the rest occurs in cytoplasm
What is the process of cutting up proteins in the muscle for use as AA in the liver referred to as?
What are the two uses of AA in muscle?
1. energy from oxidation
2. leave the muscle as alanine (or glutamine) - will go to liver
What enzyme produces the glutamine that goes from muscle to liver and what is it made from?
- glutamine synthase (plus a NH4)
What enzyme produces the alanine that migrates from muscle to liver? What is it made from?
- aminotransferase of pyruvate
What can alpha-keto acids in muscle (produced as a result of Aminotransferase) be used for?
oxidized for energy
What happens when the alanine and glutamine once in the liver after having travelled there from the muscle?
- In the liver alanine transfers NH4 back to a-ketoglutarate to form glutamate via an ATase
- Glutamine can release free NH4 and regenerate glutamate (the glutamine can also be regenerated and travel to kidney where the NH4 is released via glutaminase and the NH4 is expelled in the urine)
- now the NH4 can enter the urea cycle by forming urea in the liver and travelling to the kidney
When does a 10-20 fold induction of urea cycle enzyme synthesis occur (via genes getting turned on)? When would this occur?
- occurs when there are ammonia and aa in the liver
- In a high protein diet or at a time of high protein turnover (fasting)
How many ATP does the urea cycle use? How many high energy phosphate bonds does it split off?
What do the four carbons that enter the urea cycle as aspartate end up leaving as?
Does the urea cycle generate metabolites from which some energy can be recaptured? What metabolite and how?
- fumarate - goes through one oxi/red step and produces an NADH which goes to the ETC
What happens to urea (ie is it all expelled)?
75% expelled in urine - 25% ends up being further metabolized in GI tract
What happens to urea that enter the rumen and colon? What can happen to AA that are already there?
- bacterial urease liberates NH3 which can get integrated into bacterial protein
- AA that are already there can become bacterial protein, undergo bacterial deamination to produce NH3, or undergo decarboxylation to form toxic metabolites out in the blood stream
What are normal levels of blood ammonia? What would b considered a high concentration and what does it do?
- normally kept low (0.02 mM) by urea cycle
- High concentrations (0.2 m) are toxic to CNS