Amino Acid Degradation and the Urea Cycle - ME Flashcards
What are the most abundant amino acids in serum?
Glutamine and alanine
If methionine is low what amino acids becomes essential?
Cysteine
If phenylalanine is low what amino acids becomes essential?
Tyrosine
Patients with cystic fibrosis must be supplement with?
pancreatic enzymes
How many transporters have been identified for the transport of amino acids from the gut into intestinal epithelial cells?
5, all of which are Na or proton symporters
What is hartnups disease?
A defect in the transport system for neutral and aromatic amino acids from the gut and the renal tubules.
What are the symptoms of hartnups Disease?
Similar to pellagra (niacin deficiency, 4D’s: Diarrhea, Dermatitis, Dementia, Death)
How do you treat hartnups disease?
Administration of niacin
What is cystinuria?
A defect in the transport system for basic amino acids and cystine (a disulfide- linked dimer of cysteine) from the gut and the renal tubules.
What are some symptoms of cystinuria?
Cystine is relatively insoluble and forms crystals which can lead to urinary tract infections and kidney stones.
What amino acid is use to test muscle breakdown?
Histidine residues of the muscle protein actomyosin are methylated posttranslationally. When actomyosin is broken down, 3-methyl histidine is liberated and excreted into the urine.
Define Positive balance
If nitrogen losses are less than intake, the subject is in positive nitrogen balance, as in children and convalescing adults.
Define Negative balance
If nitrogen losses are more than intake, the subject is in negative nitrogen balance, as in diseases involving wasting or starvation.
What is kwashiorkor syndrome?
The absence of lysine in low-grade cereal proteins, used as a dietary mainstay in many underdeveloped countries, leads to an inability to synthesize protein
Free ammonia ion is highly poisonous so the body can move remove free NH + in three ways. What are the three ways?
- Glutamate Dehydrogenase
- Glutamine Synthase, reversible by Glutaminase
- Carbamoyl Phosphate Synthase I and II
What is transamination and what cofactor does it utilize?
The transfer of an amino group from an amino acid to an α-keto acid to form a new amino acid and a new keto acid.
Cofactor - Pyridoxal phosphate (vitamin b6): an essential cofactor for all transaminations.
Name all 5 reactions Pyridoxine functions as a cofactor.
1) transaminations
2) decarboxylations
3) dehydration of ß-hydroxyamino acids
4) racemizations of α-amino acids
5) removal of H2S from cysteine
Most transaminases converge what amino acid?
glutamate
Describe how the liver uses glutatmate.
Glutamate is deaminated mainly in the liver. If the liver needs energy it will generate NADH for electron transport. If it is energy rich, it will generate NADPH for biosynthetic reaction.
What are some alternate mechanisms for amino acid deamination
- Amino acid oxidases- Both L and D-amino acid oxidases occur in the kidneys and the liver.
- Direct deamination by dehydratases
- Desulfhydrases- Homocysteine desulfhydrase is also a pyridoxal phosphate containing enzyme that removes both ammonia and sulfur from homocysteine.
Name the two urea cycle enzymes compartmentalized in the mitochondrial
A. Mitchondria
carbamoylphosphate synthetase
ornithine transcarbamoylase
Name the two urea cycle enzymes compartmentalized in the cytosol
B. Cytosol
argininosuccinate synthetase argininosuccinate lyase arginase
List the 6 reactions in the urea cycle
- Carbamoylphosphate is formed from ammonia and CO2.
- Citrulline is formed from carbamoylphosphate and ornithine in a reaction that is catalyzed by ornithine transcarbamoylase (OTC).
- Argininosuccinate is formed from citrulline and aspartate.
4) Aspartate is generated arises from the transamination of oxaloacetate by glutamate. - Arginine and Fumarate are formed from the cleavage of argininosuccinate
- Urea and Ornithine are formed from the cleavage of arginine.
