Amino acid involved in urea synthesis:

Ans:B.)Aspaic Acid Urea has 2 amino (-NH2) groups, one derived from NH3 and other from aspaate.UREA CYCLE* Location: Cytosol and mitochondria of hepatocytes.* Substrates: NH 3 (as derived from oxidative deamination of glutamate); CO2 ; aspaate; three ATP.* Products: Urea; fumarate; H2O.* Purpose: The urea cycle allows for the excretion of NH 4+ by transforming ammonia into urea, which is then excreted by the kidneys.* Impoant enzymes:Carbamoyl phosphate synthetase I: Conves ammonium and bicarbonate into carbamoyl phosphate. This is the rate-limiting step in the urea cycle. This reaction requires two ATP and occurs in the mitochondria.Ornithine transcarbamoylase: Combines ornithine and carbamoyl phosphate to form citrulline. Located in mitochondria.Argininosuccinate synthetase: Condenses citrulline with aspaate to form arginosuccinate. This reaction occurs in the cytosol and requires one ATP.Argininosuccinate lyase: Splits argininosuccinate into arginine and fumarate. Occurs in the cytosol.Arginase: Cleaves arginine into one molecule of urea and ornithine in the cytosol. The ornithine is then transpoed back into the mitochondria for entry back into the cycle.* Regulation: Carbamoyl phosphate synthetase I catalyzes the rate-limiting step of the cycle and is stimulated by N -acetylglutamate.* Diseases:Hyperammonemia occurs when there is a deficiency in one of more of the urea cycle enzymes, causing insufficient removal of NH 4+ .Ammonia intoxication leads to CNS deterioration in the form of mental retardation, seizure, coma, and death.