Amino Acid Metabolism 1 Flashcards
What is pepsin?
Pepsin is a gastric enzyme that is secreted as pepsinogen by cells in the lining of the stomach. The protons in the stomach cleave pepsinogen to pepsin. Pepsin then cleaves proteins into smaller peptides before they pass to the small intestine.
- Once proteins pass from the stomach to the small intestine what 4 enzymes continue their breakdown?
- Where are these enzymes secreted from?
- trypsin, chymotrypsin, elastase, carboxypeptidase
- Pancreas
Which pancreatic protease is important for activating other pancreatic proteases?
Trypsinogen –> trypsin –> cleaves other zymogen proteases to active form
After being acted upon by pancreating enzymes, _____ on the surface of small intestine mucosal cells together with _____ inside the cells finish the digestion of proteins.
Ecoproteases
Dipeptidases
A variety of amino acid transporters use the _____ gradient to absorb the amino acids across their concentration gradient
Na+
Where is urea produced?
The liver
Under what conditions does the body perform the glucose - alanine cycle?
In the muscle: when pyruvate production outpaces the TCA cycle utilization of pyruvate, there is excess NADH produced faster than it is utilized. This inhibits PDH so the body can push pyruvate to lactate. However, this causes build up of acid which inhibits phosphofructokinase (glycolysis) so instead the muscle can make alanine, which then travels back to liver to be converted pack to pyruvate and made into glucose.
In the liver: alanine is converted back to pyruvate, which is used in gluconeogenesis to release glucose. The NH3 that is removed from alanine is eliminated as urea.
What do aminotransferases do?
Exchange amino groups between amino acids and alpha-keto acids.
What reaction does alanine aminotransferase catalyze?
Glutamate + pyruvate –> Alanine + AKG
Transfer NH2 from glutamate to pyruvate
What cofactor is needed by aminotransferases?
PLP (Vitamin B6)
Branched chain alpha-keto acids that are made in order to restore nitrogen (glutamate) in the muscle are convererted to what intermediate of the TCA cycle and by what enzyme?
Branched Chain Amino Acid Dehydrogenase converts BCAA alpha keto acids to succinyl coA. Uses same cofactors as PDH (TLCFN)
What is lost during the glucose alanine cycle and how does the muscle recoup this loss?
Nitrogen is lost because stores of glutamate are being coverted to AKG in order to convert pyruvate to alanine. As such, the muscle will preferentially degrade branched chain amino acids (Leu, Ile, Val) for their nitrogen which will be given back to AKG to make glutamate. The alpha keto acids of BCAAs that are produced by aminotransferase activity feed into the TCA cycle.
Maple Syrup Urine Disease
- Maple syrup urine disease is characterized by a defect in what enzyme?
- When does this disease present?
- How does it present?
- What would be high in the serum with this disease?
- What would be low in the serum with this disease?
- Branched chain alpha keto acid dehydrogenase
- Within 48 hours of birth
- Irritability, poor feeding, vomiting, urine that smells sweet
- Leucine, Isoleucine, valine
- Alanine
Levels of what enzyme are used as a marker for liver disease?
Alanine Aminotransferase (ALT)
How is nitrogen carried in the blood?
As glutamine
