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What are amino acid carbon skeletons (interorgan) catabolized to?
TCA cycle intermediates and ketone bodies
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When does catabolism of amino acid carbon skeletons take place?
fed and fast states
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List the places amino acid carbon skeleton catabolism takes place and what it is for?
- Liver: gluconeogenesis and ketogenesis(fasting), energy(fed)
- Muscle and intestine: energy
- Kidney: ammoniagenesis
- Brain: sythesis of nonessential amino acids
- All in mitochondria (exept for pyruvate in cytosol)
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What do the groups glucogenic, ketogenic or both glucogenic and ketogenic determine?
How the carbon skeletons are used
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How are gluconeogenic amino acid carbon skeletons used?
Enter the TCA cycle (without consuming OAA) lead to a net increase in OAA for gluconeogenesis, no need to prime the TCA cycle
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How are ketogenic amino acid carbon skeletons used?
- They form acetyl CoA of acetoacetate
- acetoacetate can't be used by the liver because it is a ketone body
- no net formation of glucose using acetyl CoA because it consumes OAA when it enters the TCA cycle
- loss of OAA requires the TCA cycle to be primed
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What are the only ketogenic amino acids?
leucine and lysine
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What are the four mutually supportive pathways that keep amino acid catabolism primarily restricted to the liver?
- Gluconeogenesis
- Amino acid catabolism (amino acids are the major precursors for gluconeogenesis so it needs to happen in the liver)
- Urea cycle (just in the liver)
- Beta-oxidation (of fatty acids supplies the energy)
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What does a high carbohydrate diet do to gluconeogenesis and the urea cycle (decrease or increase activity)?
Both gluconeogenesis and urea cycle decrease
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If a fast continues for several days and the brain is using ketone bodies what happens to gluconeogenesis and the urea cycle (decrease or increase activity)?
Both gluconeogenesis and urea cycle decrease
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Why is the urea cycle not an acidifying process?
Because amino acid carbon skeleton catabolism requires a proton that is provided by the urea cycle
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Why is plant protein less acidifying for urine than animal protein?
Animal protein has more methionine and cysteine which when catabolized generates sulfuric acid leading to an acidic urine
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Where are the three branch chain amino acids (BCAAs) metabolized?
Peripheral tissues (skeletal muscle and brain, NOT liver)
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What are the three banch chain amino acids?
leucine, isoleucine and valine
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Where is glutamine metabolized?
Kidney and small intestine
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What is the fate of leucine after it is catabolized?
Ketogenic only: acetoacetate and acetyl CoA (hint: just look at metabolic map)
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What happens to the nitrogen generated from BCAA catabolism in muscle?
The nitrogen is incorporated into alanine and glutamine (which are synthesized from the alpha amino groups removed during the initial catabolism)
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What is the fate of glutamine produced from BCAA catabolism when it reaches the kidney? Intestine?
- Kidney: converts glutamine into alpha-keto glutarate generating ammonia (ammoniagenesis) used to buffer urinary acid, any extra nitrogen is used to synthesize alanine which is then exported
- Intestine: metabolizes glutamine and releases ammonia in the GI tract, ammonia is lost in stool or absorbed to portal blood then taken up by the liver
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What is Maple syrup disease (MSD) caused by?
absence or greatly reduced activity of BCKD (leads to an accumulation of BCAAs)
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What are some of the symptoms seen in maple syrup disease (MDS)?
- elevated BCAA and alpha keto derivatives
- poor feeding
- lethargy
- cerebral edema
- vomiting
- keto acidosis
- hypoalanemia
- coma
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What is the treatement for maple syrup disease (MSD)?
relaplacing dietary protein with a mixture of amino acids low in BCAAs (gelatin)
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