Urea is end product of

(Amino acid nitrogen metabolism) (241-Harper 28th) (253-Lippincott's 4th)UREA CYCLE* Urea is the end product of protein metabolism (aminoacid metabolism) and accounts for about 90% of the nitrogen containing compounds of urine. One nitrogen of urea molecule is supplied by free NH3 and other nitrogen by aspartate. Glutamate is the immediate precursor of both ammonia. The carbon and oxygen of urea are derived from CO2. urea is produced by the liver and then is transported in the blood to the kidneys for excretion in the urine* Urea cycles occurs exclusively in the cytosol, urea is produced by the hydrolysis of arginine. The cleavage of argininosuccinate does not require ATP* Carbamoyl phosphate synthase 1 (CPS-I) is the rate limiting reaction or committed step in urea synthesisOutline of Urea cycle* The Urea cycle is linked to the TCA cycle through the productin of fumarate**, Amino acid catabolism, is therefore directly coupled to energy productionMetabolic defects in Urea cycle* Hyper ammonia type ICarbamoyl phosphate synthase I* Hyperammonia type IIOrnithine transcarbamoylase* CitrullinemiaArginosuccinate synthase* Arginosuccinic aciduriaA rginosuccinase* Hyper argininemiaArginase* Dietary consumption of a protein rich meal increases the level of N-acetylglutamate in liver which enhances urea production* Excess ammonia generated from protein nitrogen is removed by urea cycle* Excess nitrogen is removed by IV phenylacetate and benzoate that conjugate with glutamine and glycine respectively (2473-74-H17th)