a. Blood plasma analyses indicated the following: citrulline, 200 M (normal 10 –

Question

a. Blood plasma analyses indicated the following: citrulline, 200 M (normal 10 – 20 M); arginine 40 M (normal 52 – 72 ); ammonia, 1,100 M (normal 5 – 35 M); blood urea nitrogen, 1 mg/dL (normal 4-15 mg/dL). Which enzymes of the urea cycle may be deficient in the baby girl? Explain.

b. Name one amino acid that may be elevated in the blood plasma in the baby girl. Write the enzymatic reactions that lead to the elevation.

c. Despite the low production of urea, amino nitrogen can be excreted via urea cycle intermediates. Which amino acid supplement in the diet can be recommended to enhance entry of the amino nitrogen into the urea cycle? Why?

2. A baby girl appeared normal at birth but developed hyperammonaemia after 24 hours. At 56 hours, she developed focal seizure activity.

Explanation / Answer

a) Hyperammonaemia is increase in the level of ammonia in blood.

Urea is prodced from ammonia through ornithine cycle which consist of different biochemical process .

Urea is the end Product of protein metabolism.

Urea is formed from ammonia , carbon dioxide and alpha amino nitrogen of aspartate, which requires ATP.

Enzymes catalyzing the urea cycle reactions are distributed between the mitochondria and the cytosol of the liver.

The enzymeOrnithine transcarbamoylase (OTC) is deficient: OTC is found inside the mitochondria. In its presence, ornithine combines with carbamoyl phosphate to form citrulline, which is then transported out of the mitochondria. In the absence of the enzyme, accumulated carbamoyl phosphate enters the cytosol and participates in pyrimidine synthesis in the presence of CPS II(carbamoyl phosphate synthase II).

B) There is elevated levels of glutamine, formed from ammonia is seen . By increased formation of GABA from Glutamate leads to impaired neural transmission. Glutamine is produced from glutamate by glutamine synthetase, which adds NH4+ to the carboxyl group of the side chain , forming an amide.

C)Arginine spplementation can be recommended.

Sodium phenyl butyrate can also be given as supplement in diet Sodium phenylbutyrate is -oxidized to phenylacetate and the elimination of waste nitrogen is achieved by conjugating glutamine with phenylacetate in the liver and kidney to form phenylacetylglutamine .

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