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82 SECTION II BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM
Urea cycle Amino acid catabolism results in the formation Ordinarily, Careless Crappers Are Also
of common metabolites (eg, pyruvate, acetyl- Frivolous About Urination.
CoA), which serve as metabolic fuels. Excess
nitrogen generated by this process is converted
to urea and excreted by the kidneys.
CO + NH 3
2
2 ATP
Carbamoyl Citrulline Aspartate
N-acetylglutamate phosphate 2 ADP + P
(allosteric activator) synthetase I i Ornithine ATP
Carbamoyl transcarbamylase Argininosuccinate
Urea phosphate AMP + PP i
synthetase
NH NH Mitochondria
3 2 Ornithine Argininosuccinate
CO C O Cytoplasm
2
(liver)
Aspartate NH
2
To kidney Urea Arginase Argininosuccinase
H O
2
Arginine
Fumarate
Transport of ammonia by alanine
Muscle Liver
START
Amino acids Alanine Alanine
(NH ) )
(NH ) α-Ketoglutarate (NH )(NH ) (NH 3 3 α-Ketoglutarate
33
3
Cahill cycley
lucose
Glucose
Glucose Glucos
α-Ketoacids Glutamate (NH ) Pyruvate Cori cycle Pyruvate Glutamate (NH )
3
3
Lactate Lactate Urea (NH ) FINISH
3
Hyperammonemia Can be acquired (eg, liver disease) or hereditary Treatment: limit protein in diet.
(eg, urea cycle enzyme deficiencies). May be given to ammonia levels:
+
Presents with flapping tremor (eg, asterixis), Lactulose to acidify GI tract and trap NH 4
slurring of speech, somnolence, vomiting, for excretion.
cerebral edema, blurring of vision. Antibiotics (eg, rifaximin, neomycin) to
NH 3 changes relative amounts of ammoniagenic bacteria.
α-ketoglutarate, glutamate, GABA, and Benzoate, phenylacetate, or phenylbutyrate
Asterixis
glutamine to favor glutamine. CNS toxicity react with glycine or glutamine, forming
may involve GABA, α-ketoglutarate, TCA products that are excreted renally.
cycle inhibition, and cerebral edema due to
glutamine-induced osmotic shifts. NH 3 NH 3
-ketoglutarate Glutamate Glutamine
B
6
GABA
FAS1_2019_01-Biochem.indd 82 11/7/19 3:16 PM
