An amino acid used by the liver in urea cycle -
Ans. is 'c' i.e., Aspartate o Out of all amino acids involved in urea cycle aspartate is consumed.Urea cycleo Ammonia is ultimately disposed of by formation of urea by "Kreb's Henseleit urea cycle" in the liver. Urea cycle takes place both in mitochondria and cytosol. First two reactions of urea cycle occur in the mitochondria, and remaining reactions occurs in the cytosol.o Biosynthesis of urea occurs in five steps.Carbamoyl phosphate synthase-I (CPS-I), a mitochondrial enzyme, catalyzes the formation of carbamoyl phosphate by condensation of CO2. and ammonia. Two molecules of ATP are required for the reaction. CPS-I is the rate limiting enzyme of the urea cycle. It is an allosteric enzyme and allosterically activated by N-acetyl glutamateOrnithine transcarbamoylase catalyzes the formation of citrulline from carbamoyl phosphate and ornithine.Arginosuccinate synthase catalyzes the formation of arginosuccinate from citrulline and aspartate. This reaction requires lATP, but 2 high energy- phosphate bonds are consumed as ATP is converted to AMP + PPi. The amino group of aspartate provides one of the two nitrogen atoms that appear in ureaQ (The other one is provided by ammonia NH4Q).Arginosuccinate lyase (argininosuccinase) catalyses the cleavage of arginosuccinate into arginine and fumarate. Fumarate enters in TCA cycle.arginase catalyses the formation of urea from arginineQ by hydrolytic cleavage of arginine to yield urea and ornithine. Ornithine is thus regenerated and can enter mitochondria to initiate another round of the urea cycle.o The source of two nitrogen atoms of urea - one from ammoniaQ and one from amino group of aspartateQ. Source of carbon is CO2Q. Thus out of all amino acids involved in urea cycle aspartate is consumed, while there is no net loss or gain of ornithine, citrulline, arginosuccinate or arginine. There is production of fumarate as by-product.o 3 molecules of ATP are consumed (2 in first reaction and 1 in third reaction). However, 4 high energy phosphate bonds are utilized as 3rd ATP is converted to AMP+PPi.
Glutamine
Glutamate
Aspartate
Fumarate