Amino Acid Metabolism
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What does it mean to be Ammonotelic?
- Excrete ammonia (which would poison us if floating around in our bodies)
What does it mean to be Uricotelic?
- Excrete uric acid (guano)
What does it mena to be Ureotelic?
- Excrete non-toxic, water-soluble urea
- Land animals, US!
Nitrogen intake matches nitrogen excreted
Positive Nitrogen Balance
- Excess Nitrogen ingested over excreted
- eg. Pregnancy and Growth
Negative Nitrogen Balance
- Nitrogen output exceeds intake
- eg. Surgery, cancer, Kwashiorkor, Marasmus
How much total protein is turned over daily?
- 1-2% of total body protein/day turnover
- -2 other fun facts
- 75% of the liberated amino acids are reutilized
- 25% nitrogen converted to urea and carbon skeleton converted to metabolic intermediates
What can produce urea?
Glucose converted to Alanine to enter blood stream and then liver, Alanine convereted to glutamate, NH4+, and urea or Glucose to then be excreted into the blood stream.
What are the steps involved in Nitrogen catabolism?
- 1. Transamination (remove amino group)
- 2. Oxidatibe deamination of glutamate
- 3. Ammonia transport (to liver)
- 4. Reactions to the urea cycle (5 enzymes involved)
Aminotransferases catalyze transamination
amino acid + keto acid <--(aminotransferase)--> keto acid + amino acid
Alanine come from...?
Serine comes from...?
What organ are they going to and what is excreted?
- Alanine- Muscle, gut, kidney
- Serine- kidney
- Liver --->Urea, glucose
Aspartate + alpha-ketoglutarate (amino group) <---->Oxaloacetate + glutamate converted by what enzyme?
- Aspartate Aminotransferase (AST)
Alanine + alpha-ketoglutartate <---> pyruvate + glutamate converted by which enzymes?
- Alanine Aminotransferase (ALT) --->
- (SGPT) <--
Glutamate Dehydrogenase, a rate limiting enzyme in amino acid catbalism is inhibited by what?
- GTP, ATP, NADH, NADPH
- High energy
Glutamate Dehydrogenase, a rate limiting enzyme in amino acid catabolism is stimulated by what?
Serine--Serine Dehyratase--> Leads to?
Pyruvate and NH4+
Threonine --Threonine Dehyratase--> Leads to?
alpha-ketobutyrate and NH4+
Ammonia is converted to?
Where are the carbons and nitrogens from?
- Carbon from CO2
- 1 Nitrogen from Aspartate
- 1 Nitrogen from Ammonia
Where does urea cycle occur?
Parts in mitochondria and parts in cytoplasm of Liver cells
What are the amino acids is the urea cycle?
What does Aspartate become in urea cycle?
What is fumarate converted to?
Hyperammonenemia Type I
- CPSynthetase I deficiency
- 1st emzyme toxic, serious condition
Hyperornithinemia, hyperammonemia, and homocitrullinuria syndrome (HHH Syndrome)
Ornithine transporter defect
Hyperammonemia Type II
- Ornithine Transcarbamoylase deficiency
- X-linked disease
Argininosucinate synthetase deficiency
Argininosuccinase or argininosuccinate lyase deficiency
What amino acids are purely ketogenic?
What amino acids are ketogenic and glucogenic?
What enzymes are purely glucogenic?
Phenylalanine + O2 + tetrahydrobiopropterin (cofactor) oxidized by what? To What?
--Phenylalanine hydroxylase--> Tyrosine + H2O + quinonoid dihydrobiopterin
Methionine is degraded into what?
- Argininosuccinase deficiency
- Lethargy, seizures, reduced muscle tension
- Various enzymes of tyrosine degradation deficiency
- Weakness, self-mutilation. liver damage, mental retardation
- Tyrosinase deficiency
- Absence of pigmentation
- Cystathionine Beta-synthase deficiency
- Scoliosis, muscle weakness, mental retardation, thin blonde hair
- alpha-Aminoadipic semialdehyde dehydrogenase deficiency
- Seizures, mental retardation, lack of muscle tone, ataxia
Defect in reanl tubular reabsorption
Defect in renal tubular reabsorption
Cystine storage disease
hoomogentisate oxidase deficiency
Maple syrup urine disease (branched-chain ketonuria)
alpha-ketoacid decarboxylase complex defect
Classic PKU or Type 1
Types II and III
Types IV and V
- Classic PKU or Type 1- Phenylalanine hydroxylase deficiency
- Types II and III- dihydrobiopterin reductase deficiency
- Types IV and V- dihydrobiopterin biosynthesis defect cofactor not avaliable
Essential amino acids
must be obtained from diet
Nonessential amino acids
can be synthesized
What is the entry point for ammonia?
- Mitochondrial enzyme present in mammals mainly used for catabolism
- NH4+ + alpha-ketoglutarate + NAD(P)H + H+ --Glutamate dehydrogenase--> Glutamate + NAD(P)+ + H2O
Adds NH4+ to Glutamate to convert it to Clutamine
- No present in animals predominantly in plants
- 2 Glutamate generated from alpha-ketoglutarate and gluamine with the addition of NADPH
Glutamate (AA) + Pyruvate (alpha-keto acid) <----> Alpha-ketoglutarate (alpha-keto acid) + Alanine (Amino acid)
ALT a transaminase
Glutamate (AA) + Oxaloacetate (alpha-keto acid) <----> Alpha-ketoglutarate (alpha-keto acid) + Aspartate (Amino acid)
AST a transaminase
What does Transamination require?
Histidine comes from?
- Ribose 5-Phosphate
- Purely from PPP
Serine comes from?
And leads to?
- Leads to Cysteine and Glycine
Cysteine and Glycine come from?
Serine which comes from 3-Phosphoglycerate
Phenylalanine and Tryptophan come from?
What do they lead to?
- Phosphoenolpyruvate and Erthrose 4-phosphate
Aspartate comes from?
And leads to?
- Asparagine, Methionine, Threonine. Lysine
Alainine, Valine, and Leucine come from?
Glutamate comes from?
- Glutamine, Proline, Arginine
Glutamine, proline, arginine come from?
Vitamin B9 is required for?
Tetrahydrogolate formation which is needed during amino acid synthesis
One carbon groups carried by tetrahydrofolate?
- -CH3 Methyl
- -CH2- Methylene
- -CHO Formyl
- -CHNH Formimino
- -CH-- Methenyl
Intermediate oxidation state
Cysteine can be synthesized from?
- Requires SAM (ethyl donor group)
Feed back inhibition can be?
Linear and branched
Isoleucine _______ Threonine deaminase and Valine ______ it
Aspartokinase can be inhibited by what?
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