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Flashcards in Urea Cycle Deck (11)
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describe the synthesis of glutamine and alanine

  • glutamine is formed in most tissues:
    • synthesized from glutamate
    • enzyme: glutamine synthetase
  • alanine: synthesized in muscle
    • transamination from pyruvate
    • enzyme: ALT


name the reactions of the urea cycle

  1. CPS I: carbamoyl phosphate synthetase I
    • mitochondrial
    • activated by NAG
    • incorporates free ammonia
  2. OTC: ornithine transcarbamoylase
  3. ASS: argininosuccinate synthetase
  4. ASL: argininosuccinate lyase
  5. ARG: arginase


all urea cycle disorders are characterized by increased blood ______ levels and elevated blood _____ levels 

all urea cycle disorders are characterized by increased blood ammonia levels and elevated blood glutamine levels 


describe hyperammonemia type I

  • enzyme deficiency: CPS I 
  • results in hyperammonemia
  • sometimes responds to arginine intervention since Arg stimulates the formation of NAG; high levels of NAG might stimulate deficient CPS-I


describe hyperammonemia type II

  • enzyme deficiency: mitochondrial OTC 
    • normally, OTC combines ornithine and carbamoyl phosphate to form citrulline
      • citrulline is transported to the cytoplasm where it combines with aspartate to form arginosuccinate 
    • X-linked
    • most common
  • results in hyperammonemia, increased orotic acid that is excreted in urine


describe citrullinemia

  • enzyme deficiency: arginonosuccinate synthetase 
  • results in hyperammonemia, increased citrullin levels


describe argininosuccinic aciduria

  • enzyme deficiency: ASL
  • results in hyperammonemia, increased argininosuccinate levels


describe argininemia

  • enzyme deficiency: arginase 
  • results in increased arginine levels 


describe the urea cycle


what are the only 3 enzymes that can fix free ammonia?

  1. glutamate dehydrogenase
  2. glutamine synthetase
  3. CPS-I


what is the management of hyperammonemia?

  • administration of benzoic acid and/or phenylbutyrate/phenylacetate
    • benzoic acid eventually forms hippuric acid by combining with glycine
    • excreted in urine
  • low protein/high carbs
    • minimize N intake