Question

Carbamoyl phosphate synthetase I (CPS I) is present in the mitochondrial matrix.

Glutamate dehydrogenase is also present in the mitochondrial matrix. Suggest an explanation for the significance of its presence in the mitochondrial matrix.

Answer 1

◆ explanation :-

• CPS1 { ligase enzyme} is present in mitchondria which help in urea production.
• CPS1 is specific as nitrogen donar for ammonia. N acetylglutamate is required as activator
• Carbomyl phosphate synthatase enzyme catalysis ATP and bicarbonate reaction to produce carboxyphosphate
• Glutamate dehydrogenase catalysis reversible reaction of glutamate to form alpha ketogluterate and ammonia by reducing NAD(P) + to NAD(P)H .In crab cycle , alpha ketogluterate is metabolised resulting in ATP synthesis .
• From glutamine or glutamate ( with the help of glutamate dehydrogenase) , ammonia molecule is transferred to a bicarbonate molecule by CPS1 that is phosphorylated by ATP molecule .
• As a result , carbamate formed which is later phosphyrated by another ATP moleculeand forms carbomyl phosphate which left the enzyme .

◆ In CPS1 the reaction occours in 4 steps :-

• Phosphorylation of bicarbonates
• Clevage of ammonia from glutamate ( glutamate dehydrogenase) or glutamine( glutaminase)
• Attack of ammonia on carboxyphosphate , carbomate is formed.
• Phosphorylation of carbomate to form carbomyl phosphate

NOTE :-

• Only in step 2 ( glutamine is deaminated to form ammonia) , active participation of amino acid residue occurs​ .
• utilization of amino acid residue for the formation of hydrogen bond with substrate occur in other 3 steps.

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